Question

A school sent up 80 candidates for an examination and the school result was 70% pass. How many candidates should be detained so that the result becomes 80%?
A) 16
B) 12
C) 10
D) 8

Answer 1

Hint: In this question one should first calculate the values and then use the percentage applications to solve the problem. Then one should consider the unknown value as x and be able to assume that in order to solve the question we have to subtract the assumed value by the given value. Then we will get our answer.

Complete step-by-step answer:
Given the result of an examination is of 80 candidates is 70%
Then the pass candidates = $\dfrac{{70}}{{100}} \times 80 = 56$
Let x be the candidates detained so result becomes 80%
$\therefore \dfrac{{80}}{{100}} \times \left( {80 - x} \right) = 56$ (Given no. of candidates-detained candidates)
$
   \Rightarrow 640 - 8x = 560 \\
   \Rightarrow 8x = 80 \\
   \Rightarrow x = 10 \\
 $
Hence (C), is the correct option.
Note: In this question one should know the basic operations of mathematics(percentage). One can make calculation mistakes. Also, one can make the mistake in assuming the values and they have to subtract the assumed value x from the given number of candidates.