A bag of concrate can be used to make a 5ft by 7ft porch. if you want to make a 20ft by 28ft, porch. how many bags of concreate do you need? the answer is not 4

Calculate the area of each rectangular:

5x7 = 35sqft

20x28 = 560sqft

If 1 bag makes 35sqft, 560sqft is how many bags;

This is how I write the equation;

1x bag 35sqft

X 560sqft

Solution: (560x1) : 35 = 16bags

I solved this based on my way of logic. I'd appreciate if you let me know if the answer is correct.

area of 5 x 7 porch = 5*7 = 35 sq. ft.

area of 20 x 28 porch = 20 * 28 = 560 sq. ft.

560 / 35 = 16

so 16 bags are needed