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In order to simplify our calculations, we try to add numbers that give us a round result.
Keep in mind that:
Now, we get a more manageable exercise to solve:
90
\( 74+32+6+4+4=\text{?} \)
Strategic grouping makes mental math much easier! When you pair numbers like 19+21=40, you work with round numbers that are simpler to add and less likely to cause calculation errors.
Look for pairs that make multiples of 10 (like 10, 20, 30, 40). In this problem, 19+21=40 and 34+6=40. Numbers ending in 1 and 9, or 4 and 6, often pair well!
That's okay! You can still use grouping with three or more numbers. For example, if you have 7+8+13, group them as (7+13)+8 = 20+8 = 28.
No! Addition is commutative, meaning . You can rearrange and group numbers any way you want - the sum stays the same.
Add the numbers in the original order and compare. Both methods should give the same answer. For this problem: grouped method gives 90, and 19+34+21+10+6 also equals 90 ✓
For mental math, absolutely! Grouping helps you calculate quickly and accurately without tools. It's especially useful during tests where calculators aren't allowed.
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