Problem Solving

Hello,

Could someone help me to solve these problems? They are fairly simple, but they seem to stump me everytime I see them.

Thanks!

1) If the ratio of TAs to students must be 3/80, what is the maximum number of students if there are 5 TAs.
a) 130
b) 131
c) 132
d) 133
e) 134
Answer is(d)

2) A small water pump takes 2 hours to fill an empty tank. The larger pump fills the tank in half an hour. How many hours would it take both pumps at their rates to empty the tank if they being at the same time?
1) 1/4
b) 1/3
c) 2/5
d) 5/4
e) 32
Answer is (c)

3) 999/100 + 1/999
a) 10
b) -1
c) .1
d) .01
e) .001
Answer is (a)

THANKS!