Grade 10 Math · Present value
A promise, discounted
score 0

A promise, discounted

So far money has walked forwards in time, growing as it goes. Present value walks it backwards: if someone promises you FV\mathit{FV} dollars in tt years, what is that promise worth today? Undo the growth — divide by the factor instead of multiplying: PV=FV(1+r)t\mathit{PV} = \dfrac{\mathit{FV}}{(1 + r)^{t}} — read aloud: PV equals FV over one-plus-r to the t.

The idea underneath is worth keeping for life: a dollar promised for next year is worth LESS than a dollar in your hand, because the dollar in hand could be growing already. Dividing by (1+r)t(1 + r)^{t} is exactly compound interest run in reverse — same factor, opposite direction. And a free answer check: if your value-today comes out BIGGER than the promise, you multiplied when you should have divided.