Question

Robert scored 67% in maths, 78% in chemistry and 85% in physics. How many marks does he need to score in biology, so Robert's average score will be 82%?

• A. 95%
• B. 96%
• C. 97%
• D. 98%

Answer 1

The correct option is D 98%

Concept:
$\text{The number of subjects = 4}$

$\text{The average}=\frac{\text{Sum of scores in 4 subjects}}{4}$

Let Robert's score in biology be $x\%$.
Given : $\frac{67+78+85+x}{4}=82$
$\Rightarrow 67+78+85+x=82\times 4\Rightarrow 67+78+85+x=328$

$\therefore$ An algebraic equation is $67+78+85+x=328$

Put each option in the equation $67+78+85+x=328$ , Which ever satisfy the equation will be the value of x.

Option A : put $x=96\%$
$\Rightarrow 67+78+85+x=9\ne 328$
Hence, the value of x does not satisfies the equation.

Option B : put $x=96\%$
$\Rightarrow 67+78+85+96=326\ne 328$
Hence, the value of x does not satisfies the equation.

Option C : put $x=97\%$
$\Rightarrow 67+78+85+97=327\ne 328$
Hence, the value of x does not satisfies the equation.

Option D : put $x=98\%$
$\Rightarrow 67+78+85+98=328=328$
Hence, the value of x satisfies the equation.
Robert needs to score 98% in Biology to maintain the average of 82%.