In a 300m race, A beats B by 22.5m or 6 seconds. B’s time over the course is:
a) 86 seconds
b) 80 seconds
c) 76 seconds
d) None of These

Hint: We will use the unitary method to find the time taken by ‘B’ to cover 300m. It is given that A beats B by 22.5m or 6 seconds, which simply indicates the distance covered or time taken by B to complete the race. In other words, B will take 6 seconds to cover 22.5m distance and the total distance is 300m. From this, we can use the unitary method and get our answer.

Complete step-by-step answer:
It is given in the question that in a 300m race, A beats B by 22.5m or 6 seconds, then we have to find the time taken by B to complete the 300m race.
We will use a unitary method to solve this question. Basically a unitary method is a process or mathematical approach to solve a question in which we will first find the value of a single unit and then multiply it with the required value.
Since, it is given that the margin is 22.5m or 6 seconds, this means that B covers the margin in 6 seconds, that means B will cover distance of 22.5m in 6 seconds. So,
In 6 seconds, B will cover a distance of 22.5m , therefore, in 1 second, it will cover a distance of $\dfrac{22.5m}{6}$.
Now, $\dfrac{22.5m}{6}$ distance will be covered in 1 seconds, therefore 300m distance will be covered in $=300\times \dfrac{6}{22.5}=\text{80 seconds}\text{.}$
Therefore, option b) is the correct answer.

Note: We will directly find this question using formula $S=\dfrac{D}{T}$, here speed=S, D=distance, and T=time. We get time taken to cover 300m = $300\times \dfrac{D}{T}$. Therefore, it is a very basic question of unitary method, and is easy to solve, because basic calculations are involved only. The mistake in understanding the question is very common, so we must read it twice carefully and then proceed.