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 at least $60$ marks, are

Answer 1

Answer: 35

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 at least $60$ marks.
At least $60$ marks means that the marks should be greater than or equal to $60$. 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 $R.H.S$.,
$x\ge 180-145$
$\Rightarrow x\ge 35$
i.e. Ravi should get greater than or equal to $35$ marks in third unit test to get an average of at least $60$ marks.
$\therefore$ Minimum marks Ravi should get $=35$.