Your sister would be 66.
When you are 10, your sister would be 6 (10-4=6)
60 years later, you would be 70, and your sister would still be 4 years younger.
Use the hypergeometric distribution.
M=number of Men=5
F=number of women=4
m=number of men elected=2
f=number ow women elected=2.
Assuming equal chance to get elected, then
P(2M,2F)=C(M,m)*C(F,f)/C(M+F,m+f)
=C(5,2)*C(4,2)/C(9,4)
=10*6/126
=10/21
Reference: Hypergeometric distribution.

. Subtract 10x from both sides.

. Divide by 5 on both sides. x=20. So you would need to buy 20 movies.
You take 480 and divide it by 15, because it says per gallon. so then if the car goes 480 miles with 15 gallons, you have to figure out how to find per gallon. you divide 480/15 and your answer is 32