Do the math
Do the math is another way to say "think about it"...
For example: You and your friends want to go out for the evening but you only have one car and there are 9 of you.
Your friend says: Why don't we go in your car?
You say: I only have a Corolla and there are nine of us, we'd better call a taxi. You do the math.
Next time, try it out....
1 月 2018