Each month for 6 months the amount of money in a benefit fund is doubled. At the end of the 6 months there is a total of $640 in the fund. How much money was in the fund at the end of 3 months?
THe amount of money at the end of the 6 months = a x 2^6 = 640
=> a = 10
=> The amount of money at the end of 3 months = a x 2^3 = 80