2017 · Q51
The mean of 5 numbers is 15. If one more number is included, the mean of the 6 numbers becomes 17. What is the included number ?
Elementary MathematicsStatistics
- A24
- B25
- C26
- D27
Explanation
This is a mean-shift problem. Five numbers averaging 15 total 75; six numbers averaging 17 total 102. The added number is the difference of the totals: 102 - 75 = 27. The trap is option (c) 26, from subtracting the means (17 - 15 = 2) and mis-adding to 24. Hence option (d).