a desert outpost has a water supply that is sufficient to la

a desert outpost has a water supply that is sufficient to last 21 days for 15 people. At the same average rate of water consumption per person, how many days would the water supply last for 9 people?

A.28

B. 32.5

C.35

D. 37.5

E. 42.0

Please show all work to receive credit

Solution

As the number of people increases, the number of days for which the supple will last decreases

So, people = k / days

15 = k / 21

Crossmultiplying :

k = 21*15

k = 315

So, it is now people = 315 / days

For 9 people,

9 = 315 / days

days = 315/9

days = 35

So, it would last 35 days for 9 people

Option C