Chapter 11
ADDITION
Most of us find addition easier than subtraction. We will learn in this chapter how to make addition even
easier.
Some numbers are easy to add. It is easy to add numbers like 1 and 2, 10 and 20, 100 and 200, 1,000
and 2,000.
Twenty-five plus 1 is 26.
Twenty-five plus 10 is 35.
Twenty-five plus 100 is 125.
Twenty-five plus 200 is 225.
These are obviously easy, but how about adding 90? The easy way to add 90 is to add 100 and
subtract 10.
Forty-six plus 90 equals 146 minus 10. What is 146 minus 10? The answer is 136.
46 + 90 = 146 − 10 = 136
What is the easy way to add 9? Add 10 and subtract 1.
What is the easy way to add 8? Add 10 and subtract 2.
What is the easy way to add 7? Add 10 and subtract 3.
What is the easy way to add 95? Add 100 and subtract 5.
What is the easy way to add 85? Add 100 and subtract 15.
What is the easy way to add 80? Add 100 and subtract 20.
What is the easy way to add 48? Add 50 and subtract 2.
Test yourself
Try the following to see how easy this is. Call out the answers as fast as you can.
24 + 10 =
38 + 10 =
83 + 10 =
67 + 10 =
It is easy to add 10 to any number. I’m sure I don’t need to give you the answers to these.
Now, try the following problems in your head. Call out the answers as quickly as you can. Try to say
the answer in one step. For example, for 34 + 9, you wouldn’t call out, ‘Forty-four . . . forty-three,’ you
would make the adjustment while you call out the answer. You would just say, ‘Forty-three.’ Try them.
As long as you remember to add 9 by adding 10 and taking 1, add 8 by adding 10 and taking 2, and
add 7 by adding 10 and taking 3, you will find them easy.
Test yourself
Try these:
a) 25 + 9 =
b) 46 + 9 =
c) 72 + 9 =
d) 56 + 8 =
e) 37 + 8 =