Two Pipes A and B can separately fill a tank in 20 minutes and 30 minutes, respectively while a third pipe C can empty a tank in 15 minute if all the three pipes were used simultaneously in how many times will it be filled

(if f(x)=4x^2 and g(x)=x+1, find (f o g)(x)

Trish receives $450 on the first of each month. josh receives $450 on the last day of each month. both trish and josh will receive payments for next four years. at a discount rate of 9.5 percent, what is the difference in the present value of these two sets of payments?

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?