Mental Math Estimation

Add/Subtract Decimals

100

2.5 + 1.32

3.82
(3.44 - 4.20)

200

3.5 - 1.21

2.29

(2.06 - 2.52)

300

2.7 + 2.28

4.98

(4.48 - 5.48)

400

9.9 - 3.49

6.41

(5.77 - 7.05)

500

10.4 + 4.64

15.04

(13.54 - 16.54)

Add/Subtract Fractions

100

1/3 + 7/12

11/12

200

7/8 - 1/4

5/8

300

1/6 + 2/3 + 5/12

15/12 or 

1 3/12 or 

1 1/4 

(1.25)

400

11/15 - 3/5

2/15

500

1/4 + 3/8 + 1/24

16/24 or

2/3

Add/Subtract Mixed Numbers

100

1 1/4 + 3 1/2

4 3/4

200

5 1/2 - 2 1/4

3 1/4

300

2 3/4 + 1 1/2

4 1/4

400

8 1/2 - 1 1/5

7 3/10 or

7.3

500

9 2/3 + 5 1/12

14 3/4 or

14.75

Multiply/Divide Fractions or Mixed Numbers

100

1/2 of 9175

4587.5

(4128.75 - 5046.25)

200

7/8 divided by 1/2

7/4

300

2.5 x 65

162.5

(146.25 - 178.75)

400

3 3/4 X 85

318 3/4 or 318.75

(286.875 - 350.625)

500

20 divided by 2 1/2

8

Perform a Series of Operations

100

155 + 337 - 82

410

(369 - 451)

200

89 x 3 - 100

167

(150.3 - 183.7)

300

428 + 206 - 42

592

(532.8 - 651.2)

400

57 x 6 - 40

302

(271.8 - 332.2)

500

4000 x 3 - 450

11,550

(10,395 - 12,705)