In a bag there are 4 black marbles and 2 green marbles. What is the probability of choosing a black marble, not replacing it, then choosing a green marble?

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?

What is always true about a positive integer raised to a negative odd power?

With number 11 ( show how you got the answer)