Subtraction Mental Math

You can change numbers to make subtraction problems easier.

42- 28 is your problem. You will keep 42 the same, but you will need to add 2 to the 28 to make it 30.

   42-28(+2)
   42- 30
   12  (+2)     (If you add 2 at the top you must add the 2 back in)
    14

Let's try this one more time...
32-17(+3)
32-20
12+ 3
15

Now let's try one where you would subtract a number in...
55-33(-3)
55-30
25-3
22

81-14( -4)
81-10
71-4
67