41. the following table shows the number of identical black and white marbles in 3 bags.
a marble is randomly taken from bag a and put into bag b. following this, a marble is randomly taken from bag b and put into bag c. finally, a marble is taken from bag c. find the probability that the marble taken from bag c is black.
Some boys and girls were asked if they had a pet. one third of the group were boys. there were 20 boys. 20% of the girls had a pet. boys with a pet : girls with a pet = 1 : 5 i need to know how many girls there are.