​Compatible Numbers

​Compatible numbers are numbers that are easy to calculate mentally.

You can replace the values in a problem with compatible numbers so that it is easier to use mental math to compute the estimated answer.

​$.11.75 + $2.34 + $14.25 = ___

​* $11.75 and $14.25 are compatible numbers, because we know that $0.75 and $0.25 make $1, so we can mentally add $11 + $14 + $1  to get $26.00 + $2.34, which we can also add mentally since only one of the numbers has any values in the decimal places.

So, $.11.75 + $2.34 + $14.25 = $28.34

​Mental Math Example:

​24.4 + 26.7 = ___

​We know that 24 and 26 are both close to 25, and 25 + 25 = 50.

​So, 24.4 + 26.7 = About 50

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