Math question? Please help

Question

Grapefruit at a farm stand cost $3 per pound and oranges cost $4 per pound. If a shopper buys x pounds of grapefruit and y pounds of oranges, which equation represents the pounds of grapefruit and oranges that can be bought for $24?

 

A) x+y=24

B) 12xy=24

C) 4x+3y=24

D) 3x+4y=24

Answer 1

x = pounds of grapefruit

3x = cost of x pounds of grapefruit

 

y = pounds of oranges

4y = cost of y pounds of oranges

 

3x + 4y = 24

Answer 2

The important thing to do with problems like this is to get the units correct.

 

So,    $ per pound * pounds   =   $/lb * lb   = $         (the lbs cancel out)

 

The cost of grapefruit is   $3*x

The cost for oranges is   $4*y

 

So for $24 we can buy:      $3x + $4y = $24    (Answer D)