Given that 5/7 of 21 is interested in banking.
$$\frac{5}{7}\cdot21=15$$
So, 15/21 is interested in investment banking while 6 are NOT interested in investment banking.
But, we are asked to select 2 at random.
Using the logical inverse of at least one = none at all
Probability of "at least 1" want investment banking = PA
The probability that 2 do not want investment banking = P(Not A)
$$1-P\left(Not\ A\right)=PA$$
P(Not A) = Probability Inverse = (probability that 1 do not want banking) * (probability that 2 do not want banking)
$$=\frac{6}{21}\cdot\frac{5}{20}=\frac{30}{420}=\frac{3}{42}=\frac{1}{14}$$
$$PA=1-P\left(Not\ A\right)$$
$$PA=\frac{1}{1}-\frac{1}{14}=\frac{14-1}{14}=\frac{13}{14}$$

Answer = option E

15 students are interested, 6 are not interested

Prob \(= 1 - \frac{6C_2}{21C_2} = 1 - \frac{6\cdot 5}{21\cdot 20}=1 - \frac{1}{14} = \frac{13}{14}\,\Rightarrow\) __E__