Question

Find the wrong number in the series :
$7,28,63,124,215,342,511$

• A. $7$
• B. $28$
• C. $124$
• D. $215$

Answer 1

The correct option is B $28$

Clearly, the correct sequence is :
$2^3-1$, $3^3-1$, $4^3-1$, $5^3-1$, $6^3-1$, $7^3-1$, $8^3-1$.
So, 28 is wrong and should be replaced by $(3^3-1)$ i.e.26.
Hence, the answer is(B).