🔢 MathGrade 4Lesson 7
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Practice Mental Math Strategies
Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).
Learning Objectives
- 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
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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.
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.
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 landmarks that are easy multiples of 10.
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Tip: always look for the nearest multiple of 10 as your landmark. Jumping to tens makes addition and subtraction much simpler.
Vocabulary
Mental math
Solving problems in your head without writing each stepe.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 easiere.g. 8 + 5 → 10 + 3 = 13 using make-a-ten.
Decompose
Breaking a number into easier partse.g. Decompose 14 into 10 + 4 to multiply.
Doubles
A pair of the same number added together, like 6 + 6e.g. Knowing doubles to 10 speeds up mental math.
Landmark number
A friendly number such as 10, 50, or 100 used as a stepping stonee.g. 50 is a landmark when subtracting from 83.
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