We have two sets, with the terms ordered from the least to the largest:

$$ A=a_1,a_2,a_3,a_4,a_5 $$

And

$$ B=b_1,a_2,a_3,a_4,a_5 $$

And

$$ b_1>a_1 $$

Then the median ($a_3$) will be same.

Since $b_1>a_1$, the range of B ($a_5-b_1$) < the range of A ($a_5-a_1$).

Since $b_1>a_1$,

$$ Mean\ of\ B=\frac{b_1+a_2+a_3+a_4+a_5}{5} $$

$$ Mean\ of\ A=\frac{a_1+a_2+a_3+a_4+a_5}{5} $$

$$ Mean\ of\ A-Mean\ of\ B=\frac{a_1+a_2+a_3+a_4+a_5-(b_1+a_2+a_3+a_4+a_5)}{5} $$

$$ =\frac{a_1-b_1}{5}<0 $$

$$ => Mean\ of\ A-Mean\ of\ B<0 $$

$$ \therefore Mean\ of\ A<Mean\ of\ B $$

Only the mean must be greater for set B than for set A. Therefore A is correct.