Lessons · Quantitative Reasoning
CLT Quantitative Reasoning · Lesson
Averages
Average = sum ÷ count. Most average questions are easiest if you turn averages back into sums.
- Multiply each average by its count to get a sum.
- Do the arithmetic on sums (add, remove, combine).
- Divide by the new count at the end.
Q. Five numbers average 12. A sixth number is added and the average becomes 13. What is the sixth number?
Answer 18
Old sum 5 × 12 = 60; new sum 6 × 13 = 78; 78 − 60 = 18.
- Averaging two averages when the groups are different sizes. Weight each by its count.
- Confusing mean, median (the middle value in order) and mode (the most frequent).
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