himu wrote:If p = 5.18r7, what is the result when p is subtracted from p rounded to the nearest thousandth?

Algebraic Solution:
p = 5.18r7, where r is an integer such that 0 ≤ r ≤ 9

If 0 ≤ r ≤ 8, p rounded to the nearest thousandth = 5.18q, where q is an integer such that 0 ≤ q ≤ 9 and q = (r + 1)
In this case, required answer = (5.18q - 5.18r7) = 0.0003

If r = 9, p rounded to the nearest thousandth = 5.190
In this case, required answer = (5.190 - 5.1897) = 0.0003

Hence, the correct answer is D.

Tricky Solution:
Just by looking at the answer we can figure out that the answer will not depend upon the actual value of r. Hence, we can assume any value for r and solve the question.

Say, r = 0
Hence, p = 5.1807 and p rounded to the nearest thousandth = 5.181

Hence, required answer = (5.181 - 5.1807) = 0.0003

The correct answer is D.