do the math
US /duː ðə mæθ/
UK /duː ðə mæθ/
1.
to calculate or consider the facts and figures to understand the implications or outcome of a situation
:
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If you work 60 hours a week at that pay, do the math – you're barely making minimum wage.
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She said she could afford it, but when I did the math, it just didn't add up.