Topic 2, Lesson 1 Mental Math to Add

Topic 2-1: Mental Math: Find Sums and Differences

• Compensation

• Commutative Property of Addition

• Associative Property of Addition

• Break Apart

You can use compensation, a strategy that involves choosing numbers close to the actual numbers in a problem to make the computation easier, and then adjusting the answer for the numbers chosen, to find sums and differences.

• 157 + 43 + 142

• Change 157 to 160 (by taking 3 ones from 43)

• Now you have 160 + 40 + 142

• 160 + 40 = 200

• 200 + 142 is much easier! 342

You can use the Commutative Property of Addition, a strategy that states that numbers can be added in any order and the sum remains the same. For example: 15 + 35 = 35 + 15

• Commutative is like the word Community, where order should not matter. We are all friends in a community!

• Wearing shoes, gloves, or putting on socks are examples of Commutative Property, because the order in which you wear them is not important!

You can use the Associative Property of Addition, a strategy that states addends can be regrouped and the sum remains the same. We typically use this when addends are in parentheses.

• 157 + (43 + 142)

• Change the parentheses to go around 157 and 43

• Now you have (157 + 43) + 142

• 157 + 43 = 200

• 200 + 142 is much easier! 342

You can use the break apart to break up one addend in an equation into more manageable parts. For example: 157 + 43 can be broken apart in ones, tens, and hundreds.

• 157 + 43

• Break into ones, tens, and hundreds

• Now you have (100) + (50 + 40) + (7 + 3)

• 100 + 90 + 10 = 200

• Much easier!

Get a piece of paper to help you

in case you cannot solve these in your head.

Go to Schoolwork to Open EdPuzzle.

Don't forget to Mark Done when you finish EdPuzzle.

Then Open Keynote Practice Buddy.

Don't forget to Submit when you finish.