Posted by Greg on .
The side of a square box is increasing at a rate of 4mm/s and its height is increasing at a rate of 2mm/s. How fast is the volume increasing when the side is 40mm and the height is 100mm.
Can someone just tell me what formula to use?

Calculus 
Reiny,
Don't always look for a formula.
Define your variables and "create" your own formula
let the square base have sides x by x
let the height be h
Volume = x^2 h  (from V = length x width x height)
using the product rule:
d(Volume)/dt = x^2 dh/dt + h(2x) dx/dt
we are given all those values
dV/dt = 40^2 (2) + 100(80)(4)
= ....