Grade 4 - Progress in Mathematics

Mental Math

2-6

Think Think

6500 
65 hundreds

Here are some methods to help you

add and subtract mentally.

Think of tens or hundreds.

Add: 120  30 
n Subtract: 6500  400 
x

12 tens 65 hundreds

 3 tens  4 hundreds

15 tens 
 150 61 hundreds 
 6100

Look for numbers that are close to a ten

or a hundred, and use compensation.

29

 33

30

 32

62

Add 1 to 29 to make 30.

Subtract 1 from 33 to compensate.

 1

 1

Break apart numbers to find

tens and hundreds.

Think

Use the associative

property of addition.

38  14 
 a

( 30  8 )( 10  4 )

( 30  10 )( 8  4 )

40  12 
 52

8  4 
 10  2

197

 118

200

 115

315

 3

 3

144  56 
 n

Think: ( 100  44 )( 50  6 )

( 100  50 )( 44  6 )

150  50 
 200

Study these examples.

120 
12 tens

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