Sally and Marta had the same number of postcards. After Sally sold 18 of her postcards, Marta had 4 times as mow postcards as Sally. How many postcards did each girl have to begin with?
Each girl had 24 postcards.
Let the number of postcards with Sally and Marta be
After selling 18 postcards Sally had
Then Marta will have 4 times of Sally.
Adding 72 on both sides
Dividing both sides by 3
Hence each girl had 24 postcards in the beginning.