What caused the population to change after many generations

At the beginning of 1974/75,2 years a man invested #2000 in a bank at 12.5% compound interest, if it degree #650 at the end of each two years to pay his son's school fees, after payment of interest to pay his son's school fees, how much did he have left at the beginning of the 1978/79 school year?

Find the volume of the wedge cut from the first octant by the cylinder z=12-3y^2 and the plane x+y=2.

The students at jefferson middle school are raising money for a charity by selling t-shirts and hats. the number of t-shirts sold was 3 times the number of hats. the profit was $5 for each t-shirt sold and $2.50 for each hat sold. the students raised $840 for the charity. they used the system below to analyze their success and found the solution to be (144, 48). 5x+2.50y=840 x=3y how much did they earn from t-shirt sales?