Question

If two cubic feet of sand weigh 90 pound. How much do five cubic feet of sand weigh?

Answer 1

Hint: Here we are given with the weight of 2 cubic feet of sand. But we have to find the weight of 5 cubic feet. We will use a unitary method to solve this problem. In this method we will first find the weight of 1 cubic foot of sand and then multiply that weight with 5. This will give the weight of sand.

Complete step-by-step answer:
Let’s solve by unitary method. We are given the weight of two cubic feet of sand is 90 pound.
So to find the weight of 1 cubic foot we will divide 90 by 2.
Weight of 1 cubic foot of sand = \[\dfrac{{90}}{2} = 45\;pound\]
Now one foot weighs 45 pounds. To find the weight of 5 such feet we will multiply 45 by 5.
Weight of 5 cubic feet = \[45 \times 5 = 225\;pound\]
Thus this is our answer.
The weight of 5 cubic feet of sand is 225 pound.
So, the correct answer is “225 pound”.

Note: Here note that we just have to find the weight of 5 cubic feet for which weight of 2 cubic feet is helping. That is to find the weight of 1 cubic foot first. Or else we can directly calculate as,
 \[
  2{\text{ }}cubic{\text{ }}feet = 90\;pounds \\
  5{\text{ }}cubic{\text{ }}feet = ?\;pounds \;
\]
We can summarize this as,
 \[5{\text{ }}cubic{\text{ }}feet = \dfrac{{5 \times 90}}{2}\;pounds\]