Question

A pump removes 1000 gal of water from a pool at a constant rate of 50 gal/min. which equation models the amount of water y in the pool after t minutes?
a) y=50t - 1000
b) y= 50t + 1000
c) y= -50t - 1000
d) y= -50t + 1000

Answer 1

d) y= -50t + 1000 
You can re-arrange as 
The amount of water left in the pool Y = 1000 gal at the beginning minus 50 gal x number of minutes passed.  1000 - 50t (or -50t+1000)