Practice Questions
Concept Explanation
Average-based DI uses mean values from grouped data, monthly totals, or weighted combinations.
Key Formulas
- Simple average = sum ÷ count.
- Weighted average = Σ(value × weight) ÷ Σweights.
- If average of n numbers is A and one number x is added: new average = (nA + x)/(n + 1).
Example
Scores 60, 80, 100: average = 240/3 = 80.
Common Trap
Average of averages is wrong unless groups have equal size.
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Q1 EasyMonthly sales: 80, 100, 120 (Rs. lakh). Average monthly sales is:Explanation(80+100+120)/3 = 100. Hence the answer is 100.
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Q2 EasyThree months average temperature 28°C, 32°C, 30°C. Overall average is:Explanation(28+32+30)/3 = 30°C. Hence the answer is 30°C.
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Q3 EasyRuns in 4 innings: 40, 50, 60, 70. Average runs per inning is:Explanation220/4 = 55. Hence the answer is 55.
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Q4 EasyAverage of first 10 numbers is 15. Sum of first 10 numbers is:Explanation15 × 10 = 150. Hence the answer is 150.
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Q5 EasyFive days production: 50, 60, 70, 80, 90 units. Average is:Explanation350/5 = 70. Hence the answer is 70.
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Q6 EasyAverage of 5 numbers is 48. Their total is:Explanation48 × 5 = 240. Hence the answer is 240.
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Q7 EasyAverage of 40, 60, 80, 100 is:Explanation280/4 = 70. Hence the answer is 70.
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Q8 Medium10 items at Rs. 20 and 20 items at Rs. 35. Average price per item is:ExplanationTotal = 200 + 700 = 900 for 30 items. Average = 30. Hence the answer is Rs. 30.
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Q9 MediumClass A average = 70 (30 students), Class B average = 80 (20 students). Combined average is:ExplanationTotal marks = 2100 + 1600 = 3700. Combined average = 3700/50 = 74. Hence the answer is 74.
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Q10 MediumGroup of 4 averages 50; a fifth value 70 is added. New average is:ExplanationOld sum = 200. New sum = 270. Average = 270/5 = 54. Hence the answer is 54.
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Q11 MediumAverage daily sales Mon–Fri: 72, 78, 84, 90, 96. Weekly average (5 days) is:Explanation420/5 = 84. Hence the answer is 84.
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Q12 HardQuarterly revenue average Rs. 120 lakh; Q1, Q2, Q3 are 100, 110, 130. Q4 revenue is:ExplanationTotal for 4 quarters = 480. Q4 = 480 − 340 = 140. Hence the answer is Rs. 140 lakh.
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Q13 HardAverage of 6 numbers is 25. If one number 40 is replaced by 10, new average is:ExplanationOld sum = 150. New sum = 150 − 40 + 10 = 120. New average = 120/6 = 20. Hence the answer is 20.
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Q14 HardWeighted: 5 workers avg 8 hrs, 3 workers avg 10 hrs. Overall average hours is:Explanation(40+30)/8 = 70/8 = 8.75 hrs. Hence the answer is 8.75.
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DS1 Easy
What is the average of 80, 100 and 120?
Statement IThe three values are 80, 100, 120.
Statement IITheir sum is 300.
ExplanationStatement I alone: average = 100. Answer: A. -
DS2 Medium
What is the combined average of two classes?
Statement IClass A: 30 students, average 70.
Statement IIClass B: 20 students, average 80.
ExplanationNeed both class sizes and averages: combined = 74. Answer: C.
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DS3 Hard
What is Q4 revenue if quarterly average is Rs. 120 lakh?
Statement IQ1 = 100, Q2 = 110, Q3 = 130.
Statement IIAverage of four quarters is Rs. 120 lakh.
ExplanationNeed both Q1–Q3 and the average to find Q4 = 140. Answer: C. -
DS4 Hard
What is the new average after replacing 40 by 10 in six numbers averaging 25?
Statement IOriginal average of 6 numbers is 25.
Statement II40 is replaced by 10.
ExplanationNeed both facts: new average = 20. Answer: C.