Topic 8

What is the missing number?

57 + (34 + ? ) = (57 + 34) + 105

• 34

• 57

• 105

• 0

What is the missing number?

15 + 16 + 17 = ? + 16 + 15

• 16

• 17

• 15

• 14

A young tiger in a zoo weighs 383 pounds. Its sister weighs 449 pounds.

Choose all the equations that show a reasonable estimate for their total weight.

• 390 + 450 = 840

• 400 + 400 = 800

• 380 + 450 = 830

• 350 + 450 = 800

• 300 + 400 = 700

Karen wants to subtract 353 – 107 mentally.

What should she do first?

• Add 3 to 107 and add 3 to 353.

• Add 3 to 107 and subtract 3 from 353.

• Subtract 7 from 107 and subtract 3 from 353.

• Subtract 7 from 107 and add 7 to 353.

Linda wants to subtract 989 – 367 mentally.

What should she do first?

• Add 1 to 989 and subtract 1 from 367.

• Add 3 to 367 and add 1 to 990.

• Add 3 to 367 and add 3 to 989.

• Subtract 1 from 989 and add 1 to 367.

Round to the nearest ten to estimate the difference of 789 – 371.

• 780 - 380 = 400

• 800 - 400 = 400

• 800 - 370 = 430

• 790 - 370 = 420

Round to the nearest hundred to estimate the difference of 545 - 197.

• 550 - 200 = 350

• 500 - 200 = 300

• 540 - 200 = 340

• 500 - 100 = 400

What pattern is show in this addition table? Why is this true?

• Zero/Identity Property of Addition, Numbers added to zero stay the same.

• Commutative Property of Multiplication, The order of the factors can change, but the product will stay the same.

• Commutative Property of Addition, The order of the addends can change, but the sum will stay the same.

• Associative Property of Addition, The addends can be grouped in any way, but the sum will stay the same.

Doug wants to use mental math to add 413 and 351.

Which of these shows how to break apart the numbers into hundreds, tens, and ones?

• 4 + 1 + 3 and 3 + 5 + 1

• 400 + 13 and 300 + 51

• 400 + 10 + 3 and 300 + 50 + 1

• 400 + 3 and 300 + 50 + 1

Alex wants to use mental math to add 767 and 29.

Which of these shows how to break apart the numbers into hundreds, tens, and ones?

• 700 and 29

• 760 + 9 and 20 + 9

• 700 + 60 + 9 and 20 + 9

• 700 + 60 + 7 and 20 +9