a petri dish starts out with 500 bacteria. The amount of bacteria increases 25% each minute.

Y=500(25)????

nope ....

amount = 500 (1.25)^m , where is the number of minutes

(an increase of 25% results in
what you started with plus the increase
or 1 + .25 = 1.25

e.g. suppose an article costs $100
a 25% increase would be $25
so the cost is $125
that is: 100(1.25) = 125 )