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+9 |
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+1 |
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+8 |
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+2 |
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+7 |
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+3 |
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+6 |
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+4 |
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+5 |
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Going from the ends and working toward the middle you get all the 2 whole number combinations that make 10. |
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These makes- ten combinations are worth memorizing. |
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This problem is in the section of the test that allows calculators. But using mental math you can do it as fast or faster. The trick is to add up the numbers in groups that equal, 10s, 20s, 15s, in numbers that are easy to use. Look at the problem and do it as you read. 8+2 =10 11+4 =15 10 +5 = 15. Now I have 40. Add the last number and I have 42 which can be divided by 7 to get answer C. |
- When memorizing multiplication tables memorize the doubles, times five, times ten, and squares. Then memorize the rest. Doubles, times five, times ten, and squares will get you close enough to quickly add the rest.
For example 7 X 6 = 42 But if you did not know you could add 7 to 7X 5, or subtract 7 from 7 X7.
- Memorizing addition facts is easy. Start with doubles and then doubles plus one or plus two, and doubles minus one or two are close and quickly found.
For example 6+ 6 =12 so doubles plus one says 6+7=13 (see 12 plus 1) 6+8=14. 6+5 = 11(doubles minus 1).
- Dealing with plus 9 is easy. just add 10 and subtract 1.