Last year ten examiners spent 6 hours marking all the exam papers. This year the same process took only three hours.

How many examiners were there this time if they marked the same set of papers at the same rate?

20 examiners.

Step-by-step explanation:

We know that 10 examiners need 6 hours to mark all the papers.

Then if R is the rate at which one examiner can mark all the papers, we have the equation:

(10*R)*6h = marking all the papers = 1

(i will use the 1 to represent the complete task)

then we have:

(10*R)*6h = 1

60h*R = 1

R = 1/60h

This means that only one examiner would need 60 hours to mark all the papers.

This time, we have N examiners, and they marked the same amount of papers in 3 hours, then we have thee equation:

(N*R)*3h = 1

(N*1/60h)*3h = 1

N*(3h/60h) = 1

N*(1/20) = 1

N = 1/(1/20) = 20

N = 20

This time, there are 20 examiners.