Question

A water pipe can fill half of the water tank in 45 minutes. How much time will it take to fill 4 such water tanks?

Answer 1

Hint:
Here, we will multiply the time taken to fill the half-tank by 2 to find the value of the time taken to fill the whole tank and then we will multiply the time taken to fill the whole tank by 4 to compute the time needed to fill 4 tanks. Then we will use the scale for conversion from minutes to hours is \[1\min = \dfrac{1}{{60}}{\text{ hours}}\].

Complete step by step solution:
We are given that a water pipe can fill half of the water tank in 45 minutes.
Multiplying the time taken to fill the half-tank by 2 to find the value of the time taken to fill the whole tank, we get
\[ \Rightarrow 45 \times 2 = 90{\text{ minutes}}\]
Thus, the time taken to fill the whole tank is 90 minutes.
So we have to multiply the time taken to fill the whole tank by 4 to compute the time needed to fill 4 tanks, we get
\[ \Rightarrow 90 \times 4 = 360{\text{ minutes}}\]
Therefore, the time taken to fill 4 tanks is 360 minutes.
We know that when the minutes are converted into hours, the scale is used for conversion is \[1\min = \dfrac{1}{{60}}{\text{ hours}}\].
So, we will multiply the above value in minutes with \[\dfrac{1}{{60}}\], we get
\[
   \Rightarrow 360 \times \dfrac{1}{{60}}{\text{ hours}} \\
   \Rightarrow 60{\text{ hours}} \\
 \]

Hence, the time taken to fill 4 tanks is 6 hours.

Note:
Students multiply the time taken to fill 4 tanks in minutes by 100 instead of \[\dfrac{1}{{60}}\], which is wrong. It is up to us if we want to find the conversion in hours or not, but the time in hours is more preferred. Also, do not forget to write the units in the final answer.