Friendly Pairs
Part of the Numbers & Operations section of Coddy's Pre-Algebra journey. Lesson 7 of 57.
25 × 7 × 4: multiply 25 by 4 first. That makes 100. Then 100 × 7 is 700. You can do it in your head.
In a sum (adding) or a product (multiplying), you can change the order. The answer stays the same. So look for two numbers that make 10 or 100.
- 13 + 8 + 7: 13 and 7 make 20, so 28.
- 2 × 13 × 5: 2 and 5 make 10, so 130.
Challenge
You buy four things. They cost 38, 75, 62 and 25 dollars: 38 + 75 + 62 + 25. Find the total the fast way.
Try it yourself
38 + 75 + 62 + 25
Simplify the expression
All lessons in Numbers & Operations
1Order of Operations
Your First AnswerLeft to RightParentheses FirstBrackets Inside BracketsThe Fraction Bar GroupsRecap: Order of Operations4Adding Integers
Adding Two NegativesDifferent SignsZero PairsAdding Several IntegersRecap: Adding Integers5Subtracting Integers
Add the OppositeSubtracting a NegativePlus and Minus in a RowDistance Between NumbersRecap: Subtracting Integers