Exercise: Average
Questions for: Calculation of Mean
A marketing firm has two project teams. Team Alpha consists of 5 members, and their average number of client pitches last month was 12 per member. Team Beta has 3 members. If the overall average number of client pitches for all 8 team members combined was 11 last month, what was the average number of client pitches per member for Team Beta?
What was the average number of client pitches per member for Team Beta last month?
A: 9.33
B: 10.00
C: 9.00
D: 11.00
Answer: A
1. Calculate the total number of pitches made by Team Alpha: 5 members * 12 pitches/member = 60 pitches.
2. Calculate the total number of pitches made by all 8 team members combined: 8 members * 11 pitches/member = 88 pitches.
3. Determine the total number of pitches made by Team Beta by subtracting Team Alpha's total from the combined total: 88 pitches - 60 pitches = 28 pitches.
4. Calculate the average number of pitches per member for Team Beta: 28 pitches / 3 members = 9.333... pitches/member.
5. Round the average to two decimal places: 9.33.
Why others are wrong:
A — Correct answer.
B — This option results from incorrectly assuming the overall average (11) is a simple arithmetic mean of Team Alpha's average (12) and Team Beta's average (X), i.e., (12 + X) / 2 = 11, which yields X = 10. This ignores the different number of members in each team.
C — This option could be the result of rounding the correct answer down to the nearest whole number or a minor arithmetic error in calculating Team Beta's total pitches (e.g., if total was 27 instead of 28).
D — This option incorrectly assumes that Team Beta's average must be the same as the overall combined average, failing to account for Team Alpha's above-average performance which pulls the overall average up.
A regional sales manager sets a target for her team: each agent must achieve an average monthly commission of $1200 over a five-month period. Agent X's commissions for the first four months were $1100, $1350, $1050, and $1220.
What must Agent X earn in commission in the fifth month to meet the regional manager's average target?
A: $1180
B: $1200
C: $1280
D: Agent X's commissions for the first four months were $1100, $1350, $1050, and $1220.
What must Agent X earn in commission in the fifth month to meet the regional manager's average target?
A. $1180
B. $1200
C. $1280
D. $1300
Answer: C
To achieve an average of $1200 over five months, the total commission earned must be $1200 * 5 = $6000.
The total commission earned in the first four months is $1100 + $1350 + $1050 + $1220 = $4720.
To reach the target total, Agent X must earn $6000 - $4720 = $1280 in the fifth month.
Why others are wrong:
A — This is the average commission earned in the first four months, not what is needed in the fifth.
B — This is the target average itself, not the amount needed to achieve it in the final month.
D — This would be the amount needed if there was a calculation error in the sum of the first four months (e.g., if the sum was $4700 instead of $4720).
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A small business recorded the number of new clients acquired each month for the first quarter of the year. In January, they acquired 25 clients. February saw 5 fewer clients than January. March's acquisition was double that of February.
What was the average (mean) number of new clients acquired per month during this quarter?
A: 28.0 clients
B: 29.0 clients
C: 28.33 clients
D: 31.67 clients
Answer: C
1. Calculate the number of clients acquired in January: 25 clients.
2. Calculate the number of clients acquired in February: 25 - 5 = 20 clients.
3. Calculate the number of clients acquired in March: 20 * 2 = 40 clients.
4. Sum the total clients for the quarter: 25 + 20 + 40 = 85 clients.
5. Determine the number of months in the first quarter: 3 months.
6. Calculate the mean (average): Total clients / Number of months = 85 / 3 = 28.333...
7. Rounding to two decimal places, the mean is 28.33 clients.
Why others are wrong:
A — This result would occur from incorrectly rounding the mean down to the nearest whole number.
B — This result would occur from incorrectly rounding the mean up to the nearest whole number.
C — This is the correct calculation.
D — This result occurs if March's acquisition was mistakenly calculated as double January's clients (25 * 2 = 50), leading to a total of 25 + 20 + 50 = 95, and a mean of 95 / 3 = 31.67.
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A class of 15 students had an average score of 78 on a mathematics test. A new student joined the class and took the same test, resulting in the overall average score for all 16 students increasing to 79.
What was the new student's score on the mathematics test?
A: 79
B: 80
C: 94
D: 78
Answer: C
The initial total score for 15 students was 15 * 78 = 1170.
The new total score for 16 students (including the new one) is 16 * 79 = 1264.
The new student's score is the difference between the new total and the initial total.
New student's score = 1264 - 1170 = 94.
Why others are wrong:
A — This is the new average score, not the individual score of the new student.
B — This value is incorrect and would result from a miscalculation or misunderstanding of how the mean changes.
D — This is the original average score, not the individual score of the new student.
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A student took 5 tests. The average score for these 5 tests was 84. When the lowest score was removed, the average of the remaining 4 tests increased to 88.
What was the lowest score that was removed?
A: 68
B: 72
C: 76
D: 80
Answer: A
The sum of scores for all 5 tests was 84 * 5 = 420.
The sum of scores for the remaining 4 tests was 88 * 4 = 352.
The lowest score removed is the difference between these two sums.
Removed score = 420 - 352 = 68.
Why others are wrong:
A — Correct calculation.
B — Incorrect calculation, possibly a small arithmetic error in sums or subtraction.
C — Incorrect calculation, potentially subtracting a value other than the calculated difference from the initial average. For example, 84 - 8 = 76 (where 8 is twice the difference in averages).
D — Incorrect calculation, potentially subtracting the difference in averages from the initial average (84 - (88 - 84) = 84 - 4 = 80).
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