Q. The average age of 14 girls and their teacher's age is 15 yr. If teacher's age is excluded, then the average reduced by 1. What is the teacher's age? [SSC CGL 2013].
EXPLANATION
Sum of 14 girl's and teacher's age = 15x 15 = 225
Without teacer's age, sum of 14 girl's age = 14 X14 = 196
∴ Teacher's age = 225 - 196 = 29 year
Q. The average weight of 21 boys was recorded as 64 kg. If the weight of the 'teacher was added, the average increased by one kg. What was the teacher's weight? [Bank Clerks 2011 ]
EXPLANATION
Here, n = 21, a = 64 , b = 65
Weight of teacher = n(b - a) + b =21(65 - 64) + 65
= 21 + 65 = 86 kg
Q. The average age of 4 members of a family is 25 yr. If head of the family is included in this group, then average age increases by 20%. Find out the age of the head. [Delhi Police 2008]
EXPLANATION
Here n = 4, initial average a = 25
Last average b = 25 + 20% × 25
= 25 + 20 × 25 / 100
= 30
Age of the head = n (b - a) + b
= 4 (30 - 25) + 30
= 50 yr
Fast Track Practice Questions with Solutions of Average
Fast Track Techniques to solve the QUESTIONS of AVERAGE
Q. Average of ten numbers is 7. If every number is multiplied by 12, what will be the average of new numbers? [SSC (10+2) 2009]
EXPLANATION
Here initial average = 7
As we know that if all the numbers are multiplied by a certain number then their average must be a multiple of that number.
Therefore new average = 7 × 12 = 84
Q. The average of 11 numbers is 36. Out of these 11 numbers, the average of 9 numbers is 34. If the ratio of remaining two numbers is 2 : 3, find out the smaller number. [Hotel Mgmt. 2009]
EXPLANATION
Sum of 11 numbers = 36 × 11 = 396
Sum of 9 numbers = 34 × 9 = 306
Sum of remaining two numbers = 396 - 306
= 90
Therefore smaller number = 2 × 90 / ( 2+ 3)
= 180 / 5 = 36
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EXPLANATION
Sum of 14 girl's and teacher's age = 15x 15 = 225
Without teacer's age, sum of 14 girl's age = 14 X14 = 196
∴ Teacher's age = 225 - 196 = 29 year
Q. The average weight of 21 boys was recorded as 64 kg. If the weight of the 'teacher was added, the average increased by one kg. What was the teacher's weight? [Bank Clerks 2011 ]
EXPLANATION
Here, n = 21, a = 64 , b = 65
Weight of teacher = n(b - a) + b =21(65 - 64) + 65
= 21 + 65 = 86 kg
Q. The average age of 4 members of a family is 25 yr. If head of the family is included in this group, then average age increases by 20%. Find out the age of the head. [Delhi Police 2008]
EXPLANATION
Here n = 4, initial average a = 25
Last average b = 25 + 20% × 25
= 25 + 20 × 25 / 100
= 30
Age of the head = n (b - a) + b
= 4 (30 - 25) + 30
= 50 yr
Fast Track Practice Questions with Solutions of Average
Fast Track Techniques to solve the QUESTIONS of AVERAGE
Q. Average of ten numbers is 7. If every number is multiplied by 12, what will be the average of new numbers? [SSC (10+2) 2009]
EXPLANATION
Here initial average = 7
As we know that if all the numbers are multiplied by a certain number then their average must be a multiple of that number.
Therefore new average = 7 × 12 = 84
Q. The average of 11 numbers is 36. Out of these 11 numbers, the average of 9 numbers is 34. If the ratio of remaining two numbers is 2 : 3, find out the smaller number. [Hotel Mgmt. 2009]
EXPLANATION
Sum of 11 numbers = 36 × 11 = 396
Sum of 9 numbers = 34 × 9 = 306
Sum of remaining two numbers = 396 - 306
= 90
Therefore smaller number = 2 × 90 / ( 2+ 3)
= 180 / 5 = 36
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