![Subtraction Strategies
A child should know all the addition facts before attempting to master the subtraction facts to
avoid confusing the two. Some addition strategies require subtracting and some subtraction
strategies require adding. The whole point of strategies is that they be efficient and accurate.
Visual strategies are very powerful. Counting is not an efficient strategy.
Some facts can be learned with more than one strategy.
Teach the names of the strategies.
Part/whole circles
Part/whole circles. Part/whole circles, as shown below, 10 showing 10 = 4 + 6,
help children see the correlation between addition and 10 – 4 = 6, and
subtraction. The whole is written in the large circle and 10 – 6 = 4.
the parts in the smaller circles. They also help children
solve word problems. 4 6
Subtracting 1. Subtracting 1 from a number is the previous
number.
Subtracting 2. Subtracting 2 from an even number is the previous even number. Subtracting 2
from an odd number is the previous odd number.
Subtracting consecutive numbers. Explain the meaning of consecutive. The result is 1.
Subtracting from 10. These were learned first with the Go to the Dump game.
Subtracting from 9 and 11. Do these by comparing them to subtracting from 10.
The facts ≤ 10. The above strategies include all the facts with the following exceptions: 6 – 3, 7
– 3, 7 – 4, 8 – 3, 8 – 4, and 8 – 5. Two 8 facts easily can be seen with 5 as one part. The re-
maining four facts can be found with the following Going Up strategy.
Going Up < 10. The Going Up strategy works for any fact. To subtract 9 – 6, start with 6 and re-
member how much is needed to get to 9. [3] If the number being subtracted is less than 5,
Going up: 9 – 6, start at 6 and go Going up: 7 – 3, start at 3, go up
up to 9 by adding 3, the answer. to 5, then go up to 7. The answer
is 4, the total added.
first find how much is needed to go to 5 and then add the amount over 5.
Going up: 13 – 9, start at 9, go up Subtracting from 10: 15 – 9, sub-
to 10, then go up to 13. The an- tract 9 from the 10, then 1 + 5 = 6.
swer is 4, the total added.
Going Up > 10. Use the same procedure for subtracting from numbers over 10. For 13 – 9, it
takes 1 to get to 10 and 3 to get to 13; so the answer is 1 + 3 = 4. See the left figure below.
Subtracting from a 10. Subtracting 15 – 9 can be also thought of as subtracting 9 from the 10,
getting 1, and adding the result to 5 to get 6. See right figure above.
Derived strategies. Of course, there are also derived strategies. For example, if you know 12 – 6
= 6, then 13 – 6 = 7.
Doubles and near doubles. The doubles and near doubles are not very obvious in subtraction,
and therefore, not good strategies.
Info@ALabacus.com • 888-272-3291 • wwwRightStartMath.com
8-05](https://image.slidesharecdn.com/strategieshandout-111115205103-phpapp01/85/RightStart-Mathematics-Strategies-Handout-3-320.jpg)
RightStart™ Mathematics Strategies Handout
- 1. Strategies and Games for Mastering the Facts Developed by Dr. Joan A. Cotter Rote counting does not help a child master math concepts. • The alphabet example of how we teach children simple adding shows some of the difficulties. (F + E = K) 7 • Ignores place value. Yellow is the Sun • Young children don’t realize counting represents quantity. Yellow is the sun. • Very error prone. Children under 6 are not good counters. Six is five and one. • Inefficient and time-consuming. Why is the sky so blue? • No motivation to learn facts. Seven is five and two. Visualizing quantities Salty is the sea. • Babies, at 5 months, can add and subtract up to 3. Eight is five and three. • Group by 5s. Impossible to imagine 8 objects without Hear the thunder roar. grouping. Nine is five and four. • Romans grouped in 5s (VIII). • Piano music needs 10 lines, grouped in 5s. Ducks will swim and dive. Ten is five and five. Flash cards and timed tests • Based on rote learning: stimulus and response theory. • Timed tests and flash cards are a prime source of math anx- iety. Children under stress stop learning. • The only person who likes flash cards is the one who 2 5 doesn't need them. • If you do give timed tests, always let children finish the test. Ask them to graph their scores. Visual strategies for addition and subtraction facts. (See p. 2-3.) • Our visual memories are fast and permanent. 7 • Same strategy works for mental math with higher numbers. • Children who don't have a strategy will resort to counting. Why understanding is necessary. • Understanding aids memory: 93 minutes to learn earn 200 An even number. nonsense syllables, 24 minutes to learn 200 words of prose, and 10 minutes to learn 200 words of poetry. • Better learning. More motivating. • Less memorization and review needed. • Essential for applying to real problems. An odd number. • Very difficult to memorize advanced math. Using games for practice. 5 • Strategies first: It takes time for a new strategy to become automatic. Games are ideal practice. • Learn social skills and how to communicate mathematically. • No two games are the same. 3 2 Introducing subtraction. Part/part/whole. Helps • Teach after addition. It is psychologically negative. children solve problems • Part/whole circles (see figure at left) help children see the and write equations. connection between adding and subtraction. • Going up is easier for some facts; for example, 11 – 9. Used for making change. Also, avoid “take away.” Info@ALabacus.com • 888-272-3291 • wwwRightStartMath.com 8-05
- 2. Addition Strategies Strategies are a way to learn a fact or to recall a forgotten fact. These strategies are not to be taught as rules, but should be thought of a powerful visual tool. Counting should be discouraged because it is slow, often inaccurate, and unmindful of place value. Some facts can be learned with more than one strategy. Also teach the names of the strategies. Number plus 1. Adding 1 to a number is the next number. Even number plus 2. Adding 2 to an even number is the next even number. Odd number plus 2. Adding 2 to an odd number is the next odd number. Adding 5 plus numbers 1 to 4. Adding 5 to a number is obvious on fingers or the abacus. What makes 10. Enter 10 on the abacus. Separate one quantity and see what’s left. Adding 9. Enter 9 on the first wire and the other number, for example, 4 on the second wire. Take 1 from the 4 and give it to the 9 to make a ten. The sum is 10 plus 3, or 13. Adding 8. This strategy is similar to adding 9. Two beads are moved back, which is similar to counting by 2s backward. Two-fives. Both numbers need to be between 5 and 10. For example, enter 8 and 7 on two wires of the abacus. The sum is 10 plus the “leftovers,” 3 and 2. Doubles. New facts with the doubles are 3 + 3 and 4 + 4. Beyond 4 + 4 they can be seen as the Two Fives strategy. Near Doubles. New facts with the doubles are 3 + 4 and 4 + 5. Beyond 4 + 5 they can be seen as the Two Fives strategy. Relating facts. There are four facts not covered with these strategies: 6 + 3, 3 + 6, 4 + 7, and 7 + 4. They can be seen in relation to the 10's facts. Making 10: 8 + 2 = 10. Doubles: 4 + 4. Near doubles: 5 + 4. Even + 2. Odd + 2. Adding 9: 9 + 4 becomes 10 + 3. Two 5s: 8 + 7 = 10 plus 3 and 2. Relating facts. If 6 + 4 = 10, then 6 + 3 = 9. Info@ALabacus.com • 888-272-3291 • wwwRightStartMath.com
- 3. Subtraction Strategies A child should know all the addition facts before attempting to master the subtraction facts to avoid confusing the two. Some addition strategies require subtracting and some subtraction strategies require adding. The whole point of strategies is that they be efficient and accurate. Visual strategies are very powerful. Counting is not an efficient strategy. Some facts can be learned with more than one strategy. Teach the names of the strategies. Part/whole circles Part/whole circles. Part/whole circles, as shown below, 10 showing 10 = 4 + 6, help children see the correlation between addition and 10 – 4 = 6, and subtraction. The whole is written in the large circle and 10 – 6 = 4. the parts in the smaller circles. They also help children solve word problems. 4 6 Subtracting 1. Subtracting 1 from a number is the previous number. Subtracting 2. Subtracting 2 from an even number is the previous even number. Subtracting 2 from an odd number is the previous odd number. Subtracting consecutive numbers. Explain the meaning of consecutive. The result is 1. Subtracting from 10. These were learned first with the Go to the Dump game. Subtracting from 9 and 11. Do these by comparing them to subtracting from 10. The facts ≤ 10. The above strategies include all the facts with the following exceptions: 6 – 3, 7 – 3, 7 – 4, 8 – 3, 8 – 4, and 8 – 5. Two 8 facts easily can be seen with 5 as one part. The re- maining four facts can be found with the following Going Up strategy. Going Up < 10. The Going Up strategy works for any fact. To subtract 9 – 6, start with 6 and re- member how much is needed to get to 9. [3] If the number being subtracted is less than 5, Going up: 9 – 6, start at 6 and go Going up: 7 – 3, start at 3, go up up to 9 by adding 3, the answer. to 5, then go up to 7. The answer is 4, the total added. first find how much is needed to go to 5 and then add the amount over 5. Going up: 13 – 9, start at 9, go up Subtracting from 10: 15 – 9, sub- to 10, then go up to 13. The an- tract 9 from the 10, then 1 + 5 = 6. swer is 4, the total added. Going Up > 10. Use the same procedure for subtracting from numbers over 10. For 13 – 9, it takes 1 to get to 10 and 3 to get to 13; so the answer is 1 + 3 = 4. See the left figure below. Subtracting from a 10. Subtracting 15 – 9 can be also thought of as subtracting 9 from the 10, getting 1, and adding the result to 5 to get 6. See right figure above. Derived strategies. Of course, there are also derived strategies. For example, if you know 12 – 6 = 6, then 13 – 6 = 7. Doubles and near doubles. The doubles and near doubles are not very obvious in subtraction, and therefore, not good strategies. Info@ALabacus.com • 888-272-3291 • wwwRightStartMath.com 8-05
- 4. 7 Multiplication Strategies Skip counting (multiples). • Needed for multiplication facts, fractions, and algebra. 2 4 6 8 10 5 10 3 6 9 • Start as soon as 1-100 is understood; use patterns. 12 14 16 18 20 15 20 12 15 18 Skip counting pattern explanations. 25 30 21 24 27 35 40 30 • Twos. The second row is 10 plus the first row. They are the 4 8 12 16 20 even numbers. 24 28 32 36 40 45 50 7 14 21 • Threes. Consider the ones: they increase starting at the low- 28 35 42 er left with 0 (30) and continue up the first column and 6 12 18 24 30 49 56 63 over to bottom of the second column and to the third 36 42 48 54 60 70 column. Next consider the tens: 0, 1, 2 in each column. Sum of the digits: 3 in the first column (1 + 2, 2 + 1, 3 + 8 16 24 32 40 9 18 27 36 45 48 56 64 72 80 90 81 72 63 54 0), 6 in the second column, and 9 in the third. • Fours. The second row is 20 more than the first row, every Skip counting patterns. other even number. • Fives. They have an obvious singsong pattern. • Sixes. The first row is the even 3s. Second row is 30 more than the first row. • Sevens. Within each row the tens increase by 1. The ones in- crease by 1 starting at the upper right (21) and continu- ing down the column and over to the next column. • Eights. In each row the ones are the decreasing even num- bers. The second row is 40 more than the first row, also every other 4. • Nines. The sum of the digits in all cases is 9. The ones de- crease while the tens increase. The second row has the digits of the first row reversed, as shown by the arrow. Ditties • Are stored in language, not math, part of the brain. • A child who learns “6 x 1 = 6, 6 x 2 = 2, . . . “often cannot recognize multiples, which are necessary for simplifying fractions and algebra. 6 x 3 (6 taken 3 times). Multiplication seen visually on abacus. (See figures at left and below.) 7 x 5: see groups of 5s. 9 x 4 = 10 x 4 - 4. 8 x 4: four groups of 5 and 12 more. Info@ALabacus.com • 888-272-3291 • wwwRightStartMath.com 11-04
- 5. Skip Counting Patterns 1 2 3 4 5 5 10 3 6 9 6 7 8 9 10 15 20 12 15 18 25 30 21 24 27 2 4 6 8 10 35 40 30 45 50 12 14 16 18 20 7 14 21 4 8 12 16 20 28 35 42 24 28 32 36 40 49 56 63 6 12 18 24 30 70 36 42 48 54 60 8 16 24 32 40 10 20 30 40 50 48 56 64 72 80 60 70 80 90 100 9 18 27 36 45 Cut out and tape each of the 10 skip counting layouts onto 10 envelopes. In- sert into each envelope 10 cards with the same numbers as are on the envelope. 90 81 72 63 54 Info@ALabacus.com • 888-272-3291 • wwwRightStartMath.com 8-05