story problem

Question

Sally and Marta had the same number of postcards.  After Sally sold 18 of her postcards, Marta had 4 times as many postcards as sally.  How many postcards did each girl have to begin with?

Answer 1

Let x = the number of postcards that Sally and Marta started with.  Sally sold 18 postcards, so she has x-18 postcards left.  Marta still has x postcards left and now had 4 times as many cards as Sally:

 

Marta's Cards = 4*(Sally's cards)

 

x = 4(x-18)

 

x = 4x - 72

 

72 = 3x

 

Solve for x.