Arithmetic Grade Four
Lesson Thirty-seven: Addition Chains
Information:
Sometimes it's easier to group numbers to help you reach the answer more
quickly. Study this problem:
You should remember that you can re-order the numbers in an addition
problem. The problem shown above can be re-ordered like this:
This re-ordering may give you some ideas for short-cuts you can use when
adding up this problem. You should notice that 12 + 18 = 30 and that 23 + 27
= 50. To finish solving the problem once you have these sub-sums, all you
have to do is add 30, 50, and 5 for a sum of 85.
Grouping addends to form sub-sums which are multiples of ten makes it easier
to add up the whole chain of numbers. This strategy of looking for small
problems to solve within a large problem is a good way to save yourself some
time and effort.
Here's another problem for you to study:
You might notice that it is easy to add 22 + 18 to get 40 and then add 16 +
12 + 7 to get 35. Finally all you have to do is add the 40 and the 35 to get
75. Grouping numbers is one little shortcut you might find useful for some
problems.
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