The average of 25 results is 18. The average of first 12 of them is 10 and that of last 12 is 20. Find the 13th result?  Choose the most appropriate option:
A) 60  B) 75  C) 90  D) 100  E) 110

Rationale: 13 th result = sum of 25 results - sum of 24 results = 18 * 25 - 12 * 10 - 12 * 20 = 450 - 120 - 240 = 90 answer is c
Answer: C