Using patterns of 10

Using patterns of 10

To solve these types of problems, break up the numbers into groups of 10.

For example:

23+30 

break 30 into 10+10+10 

or 23 +10+10+10

count forward by 10s:

23,33,43,53

so 23+30=53

———————————–

87-20

break up 20 into 10,10

87-10-10

count back by 10s:

87,77,67