Question

Subtract the following:
  $ 3 $ hours $ 55 $ minutes from $ 7 $ hours $ 15 $ minutes

Answer 1

Hint: The given problem revolves around the concepts of basic arithmetic and unit conversion. In the given question, we are required to evaluate the difference of two time durations or quantities given to us in the problem itself. We break down the information given to us to try and identify what must be done in order to solve the problem.

Complete step-by-step answer:
Here we have to find the difference of the two time durations given to us in the problem itself.
We are given the time durations in hours and minutes format.
Now, to compute the difference, we first convert both the time durations into minutes format only and then subtract the two durations. Then, we again convert the final answer into the format of hours and minutes so as to stick to the original format of the question.
The hours and minutes are the units of time. So, we convert these time durations into minutes by using the conversion.
We know that each hour consists of sixty minutes. So, we have, $ 1hr = 60\min $ .
Now, we can convert both the time durations into minutes.
So, we have, $ 3 $ hours $ 55 $ minutes \[ = \left( {3 \times 60 + 55} \right)\min = 235\min \]
Also, we have, $ 7 $ hours $ 15 $ minutes \[ = \left( {7 \times 60 + 15} \right)\min = 435\min \]
Now, we can compute the difference easily. So, subtracting $ 3 $ hours $ 55 $ minutes from $ 7 $ hours $ 15 $ minutes, we get,
 $ \Rightarrow 435\min - 235\min $
 $ \Rightarrow 200\min $
Now, we have to convert this difference into so as to give the answer in the original format of the question.
Again, we know the unit conversion of minutes into hours as $ 1hr = 60\min $ . So, converting the difference into hours and minutes, we get,
 $ 200\min = $ $ 3 $ hours and $ 20 $ minutes.
So, we get $ 3 $ hours and $ 20 $ minutes as the result when $ 3 $ hours $ 55 $ minutes is subtracted from $ 7 $ hours $ 15 $ minutes.
So, the correct answer is “$ 3 $ hours and $ 20 $ minutes”.

Note: One must know the conversion of minutes to hours and vice versa so as to solve such types of questions. We must practice a lot of such questions so as to be able to crack these types of problems in a limited time frame. Accuracy in arithmetic is a must when doing such problems.