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Quantitative Aptitude — Average
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Quantitative Aptitude — Average

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19 mins
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23
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Quantitative Aptitude — Average — Questions with Answers Open after you finish the quiz — all 23 questions, with answers and explanations.
Q1. The average of 5 numbers is 30. If one number is excluded, the average becomes 28. What is the excluded number?
  1. 38
  2. 35
  3. 32
  4. 40
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Answer: A. 38
Total sum of 5 numbers = 5 * 30 = 150. Total sum of 4 numbers (after exclusion) = 4 * 28 = 112. Excluded number = Sum of 5 numbers - Sum of 4 numbers = 150 - 112 = 38.
Q2. What is the average of the first 7 multiples of 7?
  1. 21
  2. 28
  3. 35
  4. 42
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Answer: B. 28
The first 7 multiples of 7 are 7, 14, 21, 28, 35, 42, 49. Since these numbers are in an arithmetic progression, their average is the middle term. (7 + 49) / 2 = 56 / 2 = 28. Alternatively, Sum = 7+14+21+28+35+42+49 = 196. Average = 196 / 7 = 28.
Q3. The average age of 10 students is 15 years. If a teacher joins them, the average age increases by 1 year. What is the age of the teacher?
  1. 25 years
  2. 26 years
  3. 27 years
  4. 28 years
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Answer: C. 27 years
Total age of 10 students = 10 * 15 = 150 years. After the teacher joins, there are 11 people, and the new average age is 15 + 1 = 16 years. Total age of 11 people = 11 * 16 = 176 years. Age of the teacher = Total age of 11 people - Total age of 10 students = 176 - 150 = 26 years.
Q4. The average weight of 20 boys is 12 kg, and the average weight of 30 girls is 13 kg. What is the combined average weight of all 50 students?
  1. 12.6 kg
  2. 12.5 kg
  3. 12.8 kg
  4. 12.9 kg
Show answer
Answer: A. 12.6 kg
Total weight of 20 boys = 20 * 12 = 240 kg. Total weight of 30 girls = 30 * 13 = 390 kg. Total weight of all 50 students = 240 + 390 = 630 kg. Combined average weight = Total weight / Total number of students = 630 / 50 = 12.6 kg.
Q5. What is the average of the first five prime numbers?
  1. 5.2
  2. 5.6
  3. 6.2
  4. 6.8
Show answer
Answer: B. 5.6
The first five prime numbers are 2, 3, 5, 7, 11. Sum of these numbers = 2 + 3 + 5 + 7 + 11 = 28. Average = Sum / Number of terms = 28 / 5 = 5.6.
Q6. The average age of 5 members of a family is 28 years. If one member aged 20 years leaves the family, what will be the new average age of the remaining members?
  1. 29 years
  2. 30 years
  3. 30.5 years
  4. 31 years
Show answer
Answer: C. 30.5 years
Total age of 5 members = 5 * 28 = 140 years. After one member (20 years old) leaves, the number of members becomes 4. New total age = 140 - 20 = 120 years. New average age = New total age / Number of remaining members = 120 / 4 = 30 years.
Q7. The average of 11 results is 50. If the average of the first six results is 49 and that of the last six is 52, find the sixth result.
  1. 50
  2. 56
  3. 52
  4. 54
Show answer
Answer: B. 56
Sum of 11 results = 11 * 50 = 550. Sum of the first six results = 6 * 49 = 294. Sum of the last six results = 6 * 52 = 312. The sixth result is included in both the first six and the last six sums. Sixth result = (Sum of first six + Sum of last six) - Sum of 11 results = (294 + 312) - 550 = 606 - 550 = 56.
Q8. The average of 7 numbers is 30. If the average of the first three numbers is 28 and the average of the last three numbers is 32, what is the fourth number?
  1. 28
  2. 30
  3. 32
  4. 34
Show answer
Answer: C. 32
Total sum of 7 numbers = 7 * 30 = 210. Sum of the first three numbers = 3 * 28 = 84. Sum of the last three numbers = 3 * 32 = 96. The fourth number = Total sum of 7 numbers - (Sum of first three numbers + Sum of last three numbers) = 210 - (84 + 96) = 210 - 180 = 30.
Q9. The sum of the ages of 4 children born at the intervals of 4 years is 48. Find the age of the youngest child.
  1. 4 years
  2. 5 years
  3. 6 years
  4. 7 years
Show answer
Answer: C. 6 years
Let age of youngest = x. Then ages = x, x+4, x+8, x+12. Sum = 4x+24 = 48. So 4x = 24, x = 6.
Q10. The average ages of parents and two children are 30 years and 8 years respectively. The average age of the family is?
  1. 16 years
  2. 19 years
  3. 18 years
  4. 17 years
Show answer
Answer: B. 19 years
Sum of parents' ages = 30×2 = 60. Sum of children's ages = 8×2 = 16. Total sum = 60+16 = 76. Average of family = 76/4 = 19 years.
Q11. The average of 11 results is 50. The average of the first 6 results is 49 and that of the last 6 results is 52. What is the 6th result?
  1. 48
  2. 51
  3. 56
  4. 49
Show answer
Answer: C. 56
Sum of 11 results = 11×50 = 550. Sum of first 6 results = 6×49 = 294. Sum of last 6 results = 6×52 = 312. 6th result = (Sum of first 6 + Sum of last 6) - Sum of 11 = (294+312) - 550 = 606-550 = 56.
Q12. Surya is 25 years older than his son. In 5 years, he will be twice as old as his son. What will be Surya's age after 3 years?
  1. 20
  2. 23
  3. 45
  4. 48
Show answer
Answer: D. 48
Let son's current age = x. Surya's current age = x+25. After 5 years: Surya's age = x+25+5 = x+30, Son's age = x+5. According to the problem: x+30 = 2(x+5) => x+30 = 2x+10 => x = 20. So, son's current age = 20 years, Surya's current age = 20+25 = 45 years. Surya's age after 3 years = 45+3 = 48 years.
Q13. Runs scored by two batsmen over 7 matches are given below. Batsman 1: 42, 51, 09, 78, 63, 20, 12. Batsman 2: 30, 22, 91, 76, 84, 11, 07. Whose average was better?
  1. Batsman 1 - 39.3
  2. Batsman 1 - 45.9
  3. Batsman 1 - 43.2
  4. Batsman 2 - 45.9
Show answer
Answer: D. Batsman 2 - 45.9
Batsman 1 average = (42+51+9+78+63+20+12)/7 = 275/7 = 39.28 ≈ 39.3. Batsman 2 average = (30+22+91+76+84+11+7)/7 = 321/7 = 45.85 ≈ 45.9. Batsman 2 has a better average.
Q14. The average age of 27 students of a class is 22. If the age of the teacher is also added to their ages, then the average increases by one. Find the age of the teacher.
  1. 42
  2. 48
  3. 50
  4. 52
Show answer
Answer: C. 50
Sum of students' ages = 27×22 = 594. When teacher's age is added, total members = 27+1 = 28. New average = 22+1 = 23. New total sum of ages = 28×23 = 644. Teacher's age = New total sum - Sum of students' ages = 644 - 594 = 50 years.
Q15. In a company 10 employees get a salary of ₹36,200 each and 15 employees get a salary of ₹33,550 each. What is the average salary per employee?
  1. 34,875
  2. 34,610
  3. 27,900
  4. 36,410
Show answer
Answer: B. 34,610
Total salary for 10 employees = 36200×10 = 362000. Total salary for 15 employees = 33550×15 = 503250. Total number of employees = 10+15 = 25. Total salary = 362000 + 503250 = 865250. Average salary = 865250/25 = 34,610.
Q16. Raj scored 67, 69, 78, and 88 in 4 of his subjects. What should be his score in the 5th subject so that his average equals 80?
  1. 88
  2. 90
  3. 96
  4. 98
Show answer
Answer: D. 98
Required total score for 5 subjects to have an average of 80 = 80×5 = 400. Sum of scores in 4 subjects = 67+69+78+88 = 302. Score in the 5th subject = Required total - Sum of 4 subjects = 400-302 = 98.
Q17. Ram is 4 times his son's age today. Five years hence, Ram will be thrice his son's age. Find their current ages?
  1. 60, 15
  2. 40, 10
  3. 20, 5
  4. 32, 8
Show answer
Answer: B. 40, 10
Let son's current age = x. Ram's current age = 4x. After 5 years: Ram's age = 4x+5, Son's age = x+5. According to the problem: 4x+5 = 3(x+5) => 4x+5 = 3x+15 => x = 10. So, son's current age = 10 years, Ram's current age = 4×10 = 40 years.
Q18. The average weight of 14 students of a class is 20 kg. If a student leaves the class, the average weight of the class drops by 2 kg. Find the weight of the student (in kg) who left the class.
  1. 43
  2. 45
  3. 46
  4. 49
Show answer
Answer: C. 46
Original total weight of 14 students = 14×20 = 280 kg. After one student leaves, number of students = 13. New average weight = 20-2 = 18 kg. New total weight of 13 students = 13×18 = 234 kg. Weight of the student who left = Original total weight - New total weight = 280 - 234 = 46 kg.
Q19. A family spends ₹4,600, ₹5,600, ₹4,800, ₹3,800 and ₹6,000 on groceries in the first 5 months of a year. How much should the family spend in the 6th month to make the 6 months average spending of the family on groceries to ₹4,500?
  1. ₹2,200
  2. ₹3,650
  3. ₹4,500
  4. ₹3,500
Show answer
Answer: A. ₹2,200
Required total spending for 6 months to have an average of ₹4,500 = 6×4500 = ₹27,000. Sum of spending in the first 5 months = 4600+5600+4800+3800+6000 = ₹24,800. Spending in the 6th month = Required total - Sum of 5 months = 27000-24800 = ₹2,200.
Q20. The present average age of X, Y and Z is 44 years, 8 years ago the average age of X and Y was 38 years. What is the present age of Z?
  1. 39 years
  2. 38 years
  3. 41 years
  4. 40 years
Show answer
Answer: D. 40 years
Present total age of X, Y, Z = 3×44 = 132 years. 8 years ago, average age of X and Y was 38 years. So, 8 years ago, total age of X and Y = 2×38 = 76 years. Present total age of X and Y = 76 + (8×2) = 76 + 16 = 92 years. Present age of Z = Present total age of X, Y, Z - Present total age of X and Y = 132 - 92 = 40 years.
Q21. Five years ago, ages of father and his son were in the ratio 7:2. Five years hence, ages of the father and his son will be in the ratio 9:4. After how many years will the father's age be twice the age of his son?
  1. 8
  2. 12
  3. 9
  4. 10
Show answer
Answer: D. 10
5 years ago: Father's age = 7x, Son's age = 2x. Present ages: Father = 7x+5, Son = 2x+5. 5 years hence: Father = 7x+10, Son = 2x+10. Given ratio: (7x+10)/(2x+10) = 9/4. Cross-multiply: 4(7x+10) = 9(2x+10) => 28x+40 = 18x+90 => 10x = 50 => x = 5. Present ages: Father = 7(5)+5 = 40 years, Son = 2(5)+5 = 15 years. Let 'a' be the number of years after which father's age will be twice the son's age. 40+a = 2(15+a) => 40+a = 30+2a => a = 10 years.
Q22. What is the third number in a group of three numbers with a combined average of 29, when the average of the other two numbers is 13?
  1. 61
  2. 30
  3. 28
  4. 34
Show answer
Answer: A. 61
Total sum of 3 numbers = 3×29 = 87. Sum of the other two numbers = 2×13 = 26. Third number = Total sum of 3 numbers - Sum of 2 numbers = 87-26 = 61.
Q23. Narendra's mother is four times as old as Narendra. Four years ago, his mother was six times as old as Narendra was. What are their Present ages?
  1. 10 years, 40 years
  2. 7 years, 28 years
  3. 20 years, 80 years
  4. 5 years, 20 years
Show answer
Answer: A. 10 years, 40 years
Let Narendra's present age = x. Mother's present age = 4x. Four years ago: Narendra's age = x-4, Mother's age = 4x-4. According to the problem: 4x-4 = 6(x-4) => 4x-4 = 6x-24 => 2x = 20 => x = 10. So, Narendra's present age = 10 years, Mother's present age = 4×10 = 40 years.
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