Mathematics — Standard (041) — CBSE Class 10 board question

Option B: 10

Let the three numbers in A.P. be $a-d,\ a,\ a+d$. Their sum $= 3a = 30$, so $a = 10$. The middle term is 10.

The standard trick for three numbers in A.P. is to take them as $a-d, a, a+d$. The $d$ cancels on adding, giving $3a =$ sum directly. The middle term equals $\frac{\text{sum}}{3} = \frac{30}{3} = 10$.