Average
- The average of a, b and c is 20 and that of b, c and d is 25. If d = 30, then the value of a is :
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According to the question,
a + b + c = 3 × 20 = 60 ...(i)
b + c + d = 3 × 25 = 75 ...(ii)
By equation (i) – (ii),
a – d = 60 – 75
⇒ a – 30 = – 15Correct Option: D
According to the question,
a + b + c = 3 × 20 = 60 ...(i)
b + c + d = 3 × 25 = 75 ...(ii)
By equation (i) – (ii),
a – d = 60 – 75
⇒ a – 30 = – 15
⇒ a = 30 – 15 = 15
- The average of makrs of 17 students in an examination was calculated as 71. But it was later found that the mark of one student had been wrongly entered as 65 instead of 56 and another as 24 instead of 50. The correct average is
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Total correct marks of 17 students = 17 × 71 – 65 – 24 + 56 + 50
Total correct marks of 17 students = 1207 – 89 + 106 = 1224∴ Required correct average = 1224 17
Correct Option: C
Total correct marks of 17 students = 17 × 71 – 65 – 24 + 56 + 50
Total correct marks of 17 students = 1207 – 89 + 106 = 1224∴ Required correct average = 1224 = 72 17
- The average of 12 numbers is 9. If each number is multiplied by 2 and added to 3, the average of the new set of numbers is
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If each number of a set be multiplied by m, the average gets multiplied by m.
If each number of a set be increased by p, the average gets increased by p.
Here , The average of 12 numbers = 9
m = 2 , p = 3Correct Option: C
If each number of a set be multiplied by m, the average gets multiplied by m.
If each number of a set be increased by p, the average gets increased by p.
Here , The average of 12 numbers = 9
m = 2 , p = 3
∴ Required average = m × The average of 12 numbers + p = 2 × 9 + 3 = 21
- A librarian purchased 50 story– books for his library. But he saw that he could get14 more books by spending Rs. 76 more and the average price per book would be reduced by Re. 1. The average price (in Rs.) of each book he bought, was :
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Let the average cost of each book bought (of 64 books) be ₹ y.
According to the question,
64 × y – 50(y + 1) = 76
⇒ 64y – 50y – 50 = 76
⇒ 14y = 76 + 50 = 126Correct Option: B
Let the average cost of each book bought (of 64 books) be ₹ y.
According to the question,
64 × y – 50(y + 1) = 76
⇒ 64y – 50y – 50 = 76
⇒ 14y = 76 + 50 = 126⇒ y = 126 = 9 14
∴ Required average price = 9 + 1 = ₹ 10
- In a class, average height of all students is ‘a’ cms. Among them, average height of 10 students is ‘b’ cms and the average height of the remaining students is ‘c’ cms. Find the number of students in the class. (Here a > c and b > c )
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Let the total number of students in the class be n.
According to the question,
an = 10 × b + (n – 10) c
⇒ an = 10b + nc – 10c
⇒ an – cn = 10b – 10c
⇒ n (a – c) = 10 (b – c)Correct Option: D
Let the total number of students in the class be n.
According to the question,
an = 10 × b + (n – 10) c
⇒ an = 10b + nc – 10c
⇒ an – cn = 10b – 10c
⇒ n (a – c) = 10 (b – c)⇒ n = 10 (b - c ) ( a - c )
