2-52 Adding and Subtracting Horizontally

Adding and subtracting horizontally is easy.

46 can be written as 40 + 6 and 23 can be written as 20 + 3.

Add the ONES first.  6 + 3 = 9

Then add the TENS.   40 + 20 = 60

So the sum is 60 + 9 or 69.

The same method can be used to subtract two-digit numbers.

Find the difference of 56 - 32.

Subtract the ONES first.  6 - 2 = 4

Then subtract the TENS.  50 - 30 = 20

So the difference is 20 + 4 or 24.

Find the sum.

26 + 33 = (20 + 6) + (30 + 3) = (20 + 30) + (6 + 3) = 50 + 9 = 59

32 + 45 = (30 + ) + (40 + ) = (30 + 40) + (2 + ) = 70 + 7 = 77

43 + 21 = ( + 3) + (20 + ) = (40 + ) + (3 + ) =  + 4 = 64

15 + 13 = ( + 5) + ( + 3) = (10 + ) + ( 5 + 3) = + 8 = 28

64 + 25 = ( + 4) + (20 + ) = ( + 20) + (4 + 5) = 80 + 9 =

14 + 73 = (10 + ) + (70 + ) = (10 + ) + (4 + ) = + 7 = 87

28 + 51 = ( + 8) + ( + 1) = (20 + 50) + (8 + ) = + 9 = 79

Find the difference.

57 - 33 = (50 - 30) + (7 - 3) = 20 + 4 = 24

35 - 21 = ( - 20) + (5 - ) = 10 + 4 = 14

27 - 12 = (20 - ) + (7 - ) = 10 + = 15

68 - 32 = ( - 30) + ( - 2) = + 6 =

98 - 77 = ( - 70) + (8 - ) = + 1 =