Subtract 100 to get 332. Add 13 (add 10 and then 3) to get 345. Easy.Test yourself
Try these problems in your head. You can write down the answers.
a) 86 − 38 =
b) 42 − 9 =
c) 184 − 57 =
d) 423 − 70 =
e) 651 – 185 =
f) 3,424 − 1,895 =
The answers are:
a) 48
b) 33
c) 127
d) 353
e) 466
f) 1,529
For a) you would subtract 40 and add 2.
For b) you would subtract 10 and add 1.
For c) you would subtract 60 and add 3.
For d) you would subtract 100 and add 30.
For e) you would subtract 200 and add 15.
For f) you would subtract 2,000 and add 100, then 5.
In each case there is an easy subtraction and the rest is addition.Numbers around 100
When we subtract a number just below 100 from a number just above 100, there is an easy method. You
can draw a circle below the number you are subtracting and write in the amount you need to make 100.
Then add the number in the circle to the amount the first number is above 100. This turns subtraction
into addition.
Let’s try one.
Seventy-five is 25 below 100. Add 25 to 23 for an easy answer of 48. Let’s try another.This technique works for any numbers above and below any hundreds value.