Mental Math: 10 more than Mental Math: 10 less than Add Tens Subtract Tens Add Tens to a Number
100
68
58 + 10 =
100
14
24 - 10 =
200
6 tens + 2 tens = 8 tens
so
60 + 20 = 80
60 + 20 =
100
2 tens - 1 ten = 1 ten
so
20 - 10 = 10
20 - 10 =
100
1 ten +1 ten + 1 one = 2 tens and 1 one
so
10 + 11 = 21
10 + 11 =
200
39
29 + 10 =
200
21
31 - 10 =
200
3 tens + 5 tens = 8 tens
so
30 + 50 = 80
30 + 50 =
200
7 tens - 4 tens = 3 tens
so
70 - 40 = 30
70 - 40 =
200
8 tens + 1 ten + 2 ones = 9 tens and 2 ones
so
80 + 12 = 92
80 + 12 =
300
17
10 + 7 =
300
85
95 - 10 =
300
4 tens + 5 tens = 9 tens
so
40 + 50 = 90
40 + 50 =
300
9 tens - 4 tens = 5 tens
so
90 - 40 = 50
90 - 40 =
300
4 tens + 1 ten + 7 ones = 5 tens and 7 ones
so
40 + 17 = 57
40 + 17 =
400
10
47 + _____ = 57
400
33
____ - 10 = 43
400
9 tens - 3 tens = 6 tens
so
60 + 30 = 90
____ + 30 = 90
400
8 tens - 2 tens = 6 tens
so
80 - 20 = 60
80 - _____ = 60
400
2 tens + 7 ones + 5 tens = 7 tens and 7 ones
so
27 + 50 = 77
27 + 50 =
500
10
84 + _____ = 94
500
17
____ - 10 = 7
500
6 tens + 4 tens = 10 tens
so
60 + 40 = 100
60 + _____ = 100
500
10 tens - 7 tens = 3 tens
so
100 - 70 = 30
100 - 70 =
500
8 tens + 9 ones + 1 ten = 9 tens and 9 ones
so
89 + 10 = 99
89 + 10 =






Chapter 8 Review

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