Average
- The average weight of A, B and C is 45 kg. If the average weight of A and B be 40 kg and that of B and C be 43 kg, then the weight of B is :
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B’s weight = (A + B)’s weight + (B + C)’s weight – (A + B + C)’s weight
B’s weight = (40 × 2 + 2 × 43 – 45 × 3) kg.
B’s weight = (80 + 86 – 135) kg.Correct Option: A
B’s weight = (A + B)’s weight + (B + C)’s weight – (A + B + C)’s weight
B’s weight = (40 × 2 + 2 × 43 – 45 × 3) kg.
B’s weight = (80 + 86 – 135) kg.
B’s weight = 31 kg.
- The average of marks obtained by 100 candidates in a certain examination is 30. If the average marks of passed candidates is 35 and that of the failed candidates is 10, what is the number of candidates who passed the examination?
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Number of successful students in the exam = p
∴ Number of unsuccessful students = 100 – p
According to the question,∴ 30 = 35p + 10(100 - p) 100
⇒ 3000 = 35p + 1000 – 10p
⇒ 3000 = 25p + 1000
⇒ 25p = 3000 – 1000 = 2000
Correct Option: C
According to the question,
∴ 30 = 35p + 10(100 - p) 100
⇒ 3000 = 35p + 1000 – 10p
⇒ 3000 = 25p + 1000
⇒ 25p = 3000 – 1000 = 2000⇒ p = 2000 = 80 25
- The average weight of 8 persons increases by 2.5 kg when a new person comes in place of one of them weighing 65 kg. The weight of the new person is
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Weight of new person = (65 + 8 × 2.5) kg
Weight of new person = (65 + 20) kg = 85 kg
Aliter : Using Rule 23,
Here, x = 2.5, n = 8
Weight of new person = [ weight of replaced boy + x × n ]Correct Option: B
Weight of new person = (65 + 8 × 2.5) kg
Weight of new person = (65 + 20) kg = 85 kg
Aliter : Using Rule 23,
Here, x = 2.5, n = 8
Weight of new person = [ weight of replaced boy + x × n ]
Hence , Weight of new person = [ 65 + 2.5 × 8 ] = (65 + 20) kg = 85 kg
- The average of 1, 3, 5, 7, 9, 11, -------- to 25 terms is
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Sum of first n odd natural numbers = n²
∴ Their average = n² = n n
Correct Option: B
Sum of first n odd natural numbers = n²
∴ Their average = n² = n n
∴ Required average = 25 , because n = 25
- Six friends have an average height of 167 cms. A boy with height 162 cm leaves the group. Find the new average height.
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Total height of 5 friends = (6 × 167 – 162) cm.
Total height of 5 friends = (1002 – 162) cm.
Total height of 5 friends = 840 cm.Correct Option: A
Total height of 5 friends = (6 × 167 – 162) cm.
Total height of 5 friends = (1002 – 162) cm.
Total height of 5 friends = 840 cm.∴ Required average = 840 = 168 cm. 5
