Practice Mental Math Strategies
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What you will learn
- 1Apply the make-a-ten strategy to add mentally
- 2Use the break-apart (decomposition) strategy to multiply mentally
- 3Apply doubles and near-doubles to speed up mental addition
- 4Choose the most efficient mental math strategy for a given problem
Mini Lesson
Mental math strategies let you solve number problems quickly in your head without writing every step. Knowing which strategy to use — and why — makes you a more flexible and confident mathematician.
Make-a-Ten Strategy
- Find how much is needed to reach the next round ten.
- 47 + 36: add 3 to 47 to make 50, then add the remaining 33. 50 + 33 = 83.
- Works best when one addend is close to a multiple of 10, or of 100 (make-a-hundred: 98 + 25 → 100 + 23 = 123).
Break-Apart (Decompose) Strategy
- Split one number into parts that are easier to work with.
- 6 x 14: break 14 into 10 + 4. Then 6x10 = 60 and 6x4 = 24. Add: 60 + 24 = 84.
- Works well for multiplying a 1-digit number by a 2-digit number, and you can also break apart with a minus (3 x 29 = 3 x 30 - 3 = 87).
Doubles and Near-Doubles
- Doubles: 8 + 8 = 16. Memorize these for instant recall.
- Near-doubles: 8 + 9 = double 8 + 1 = 16 + 1 = 17.
- Use near-doubles whenever two addends differ by 1.
Jump Strategy for Subtraction
- Jump forward from the smaller number to the larger, counting the hops.
- 83 - 47: jump 3 from 47 to 50 (landmark), then jump 33 more to 83. Total jumps: 3 + 33 = 36.
- Choose landmark numbers that are easy multiples of 10.
Words to know
Mental math
Solving problems in your head without writing each step
e.g. I used mental math to add 28 + 7 quickly.
Make-a-ten
Adjusting an addend to a multiple of 10 to make the sum easier
e.g. 8 + 5 → 10 + 3 = 13 using make-a-ten.
Decompose
Breaking a number into easier parts
e.g. Decompose 14 into 10 + 4 to multiply.
Doubles
A pair of the same number added together, like 6 + 6
e.g. Knowing doubles to 10 speeds up mental math.
Landmark number
A friendly number such as 10, 50, or 100 used as a stepping stone
e.g. 50 is a landmark when subtracting from 83.
Tip: always look for the nearest multiple of 10 as your landmark. Jumping to tens makes addition and subtraction much simpler.
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