Find the wrong number in the following number series.

$81, 50, 25, 9, 1$

Find the wrong number in the following number series.

$99, 51, 22, 15, 9, 6$

Find the wrong number in the following number series.

$128, 64, 30, 16, 8$

The average weight of A, B and C is $50 kg$. The average weight of A and B is $45 kg$ and that of B and C is $55 kg$. What is the weight of B?

Find the approximate value which will come in place of the question mark (?) in the following question.

$\frac{17}{5} + \frac{23}{7} – \frac{33}{16} = ?$