Adding Subtracting Mentally

How many more red and green marbles are in the collection than blue and yellow marbles?

• 80

• 100

• 74

• 200

Use mental math to compute your answer:
120- 33

• 87

• 93

• 97

• 83

Use mental math to compute your answer:
103- 79

• 25

• 24

• 178

• 182

Garry's Work 
422- 145- 45
422- (145- 45)
422- 100
322
Do you agree with Garry's work? Explain. 

• Yes, his work does seem to follow along with the correct order, and the answer is 322. 

• No, he needs to use a different strategy. He should have 422-145= 277, and then 277- 45 to get  the answer 232.

• No, he should have rounded 422 to 400, rounded 145 to 150, and rounded 45 to 50 to find the answer of 200

2 3/5 - 3/4 + 2/5

• 1 1/4

• 4 1/4

• 3 1/4

• 2 1/4

1 3/4 + 1/2 + 1/4+ 1/2

• 2

• 3

• 4

• 1

5/6 + 1/3 - 4/3 + 1/6

• 1

• 2

• 3

• 0

50 + 50

• 250

• 100

• 300

• 50

120 + 120

• 230

• 250

• 220

• 240

78 + 15

• 93

• 92

• 91

• 90