Question

Ravi obtained $70$ and $75$ marks in first two unit tests. Then, the minimum marks he should get in the third test to have an average of atleast $60$ marks, are

• A. 45
• B. 35
• C. 25
• D. None of these

Answer 1

Answer: (B)

Let Ravi got $x$ marks in third unit test.
$\therefore$ Average marks obtained by Ravi
$=\frac{\text{ Sum of marks in all tests }}{\text{ Number of tests }}$
$=\frac{70+75+x}{3}=\frac{145+x}{3}$
Now, it is given that he wants to obtain an average of atleast 60 marks.
Atleast 60 marks means that the marks should be greater than or equal to 60 .
$\text{ i.e., }\frac{145+x}{3}\ge 60$
$\Rightarrow 145+x\ge 60\times 3$
$\Rightarrow 145+x\ge 180$
Now, transferring the term 145 to $RHS$,
$x\ge 180-145$
$\Rightarrow x\ge 35$
i.e., Ravi should get greater than or equal to 35 marks in third unit test to get an average of atleast 60 marks.
$\therefore$ Minimum marks Ravi should get $=35$