In a group of 62 students, 42 take Mathematics, 38 take Physics, and 40 take Chemistry. 20 take Math and Physics, 25 take Math and Chemistry, and 28 take Physics and Chemistry. 18 students take all th

The number of students who take Mathematics but neither Physics nor Chemistry is 15.

b) Number of students who take Chemistry only.
This is represented by $N(C \text{ only})$.

The number of students who take Chemistry only is 5.

c) Number of students who take at least one of the three subjects.
This is represented by $N(M \cup P \cup C)$.

The number of students who take at least one of the three subjects is 65.

d) Number of students who take none of the three subjects.
This is represented by $N(U) - N(M \cup P \cup C)$.

This result indicates an inconsistency in the provided data, as the number of students taking none of the subjects cannot be negative. It implies that the sum of students taking at least one subject (65) is greater than the total number of students (62).

Let's re-check the calculations for part (c) to ensure accuracy.
$N(M \cup P \cup C) = 42 + 38 + 40 - 20 - 25 - 28 + 18$
$N(M \cup P \cup C) = (42+38+40) - (20+25+28) + 18$
$N(M \cup P \cup C) = 120 - 73 + 18$
$N(M \cup P \cup C) = 47 + 18 = 65$

The calculation for part (c) is correct based on the given numbers. The negative result in part (d) suggests that the problem statement contains inconsistent data. However, if we must provide an answer based on the given numbers, the calculation leads to -3. Since the number of students cannot be negative, this indicates an issue with the problem's input values.

Assuming the question expects a numerical answer based on the provided data, even if it leads to an impossible real-world scenario:
The number of students who take none of the three subjects is $\boxed{-3}$.