Saturday, July 19, 2008

Mental Math Strategies, compatible numbers- Singapore Math

This is a strategy that I think a lot of people use, without realizing that they do it.

In this strategy you look for compatible numbers, or two numbers that you can add, together to reach a ten.

For example:

17 + 379 + 13=

the 7 and the 3 are compatible and add to make an additional 10 turning the problem into

10 + 379 + 10 + 10=

or

379 + 30 = 409


Another example:

42 + 612 + 18 =

the 2 in 42 and the 8 in 18 are compatible, making

40 + 10 + 10 + 612 = 60 + 612 = 672

Or another way to do it is using the left to right method:

12 + 16

break out your addends to their place values:

(10+10) + (2+6)

finish adding
20 + 8 = 28


another example

25 + 23

(20 + 20) + (5 + 3)

40 + 8

48
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