alleryFind the average of $5, 10, 15, 20$ and $25$.
- $12$
- $14$
- $15$
- $17$
Show answer and solution
Correct answer: C. $15$
Sum $= 5+10+15+20+25 = 75$.
Average $= \dfrac{75}{5} = 15$.
GMAT Averages — practice questions
Explore 12 free Averages questions in GMAT Quantitative Reasoning. Open each question or exercise to read its content, reference answers and available explanation.
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Showing questions 1–12 of 12.
Find the average of $5, 10, 15, 20$ and $25$.Read the answer and worked solution →What is the average of the first five natural numbers?Read the answer and worked solution →The average of $11$ numbers is $50$. If the average of the first six is $49$ and that of the last six is $52$, find the sixth number.Read the answer and worked solution →The average weight of A, B and C is $45$ kg. The average of A and B is $40$ kg, and the average of B and C is $43$ kg. Find B's weight.Read the answer and worked solution →The average of 5 numbers is 24. Their sum is:Read the answer and worked solution →A class has 40 boys averaging 65 marks and 20 girls averaging 80 marks. What is the overall average?Read the answer and worked solution →A car travels 60 km at 30 km/h and returns 60 km at 60 km/h. What is the average speed for the round trip?Read the answer and worked solution →The average of 9 numbers is 50. When the largest number is removed, the average drops to 48. What was the largest?Read the answer and worked solution →The average of 5 marks is 72. Four of the marks are 65, 70, 75 and 80. What is the fifth mark?Read the answer and worked solution →A class of 30 students has average marks 60. A new student joins and the average rises to 61. The new student scored:Read the answer and worked solution →A cricketer's average for the first 10 innings was 35. In his 11th innings he scored 79 runs. His new average is:Read the answer and worked solution →Class A has 25 students averaging 70 marks. Class B has 35 students averaging 60 marks. What is the combined average?Read the answer and worked solution →
Worked practice questions
What is the average of the first five natural numbers?
- $2$
- $2.5$
- $3$
- $3.5$
Show answer and solution
Correct answer: C. $3$
Sum $= 1+2+3+4+5 = 15$.
Average $= \dfrac{15}{5} = 3$.
The average of $11$ numbers is $50$. If the average of the first six is $49$ and that of the last six is $52$, find the sixth number.
- $52$
- $54$
- $56$
- $58$
Show answer and solution
Correct answer: C. $56$
**Set up.** Total of all $11$ numbers $= 11 \times 50 = 550$. Sum of first six $= 6 \times 49 = 294$. Sum of last six $= 6 \times 52 = 312$.
**Key observation.** The sixth number is counted in both groups (it's the last of the first six *and* the first of the last six). So $294 + 312 = 606 = \text{sum of all 11} + \text{sixth number}$.
**Solve.** Sixth number $= 606 - 550 = 56$.
**Why option A (52) is tempting.** Picking the average of the second group directly ignores the overlap
the sixth number is *systematically pulled toward whichever group has the higher mean* relative to the overall mean.
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