Jill made some cookies. Jill gave 1/4 of her cookies to Bob. Then Jill gave 1/2 of the remaining cookies to Joe. At this point, Jill had 18 cookies left. How many cookies did Jill have at first?

Answer 1

T total cookies

T-(Tx1/4) - ((T-(Tx1/4))x1/2) =18
T-T/4 - 3T/4 x 1/2= 18
3T/4-3T/8=18
3T/8=18
3T=144
T=48

Answer 2

or,
after giving (1/4)T away, she has (3/4)T left
after giving 1/2 of those away, she has (1/2)(3/4)T or (3/8)T left

3T/8 = 18
3T = 144
T = 48