Question

Omar paved a 6 foot walkway using 20 stones. He now wants to extend the walkway to 9 feet. How many more stones will he need to buy?

Answer 1

Number of stones needed = [(9-6)/6] x 20 = (20/2) stones = 10 stones

Answer 2

Set up a proportion:
6/20 = 9/x
x will be the total number of stones. Then perform x-20 to get the number of additional stones to buy. Notice that x is the number of stones needed for 9 ft,
Since we already had stones for 6 ft,
=> We only need x - 20 stones MORE :)