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Maths Quiz for DSSSB & KVS/NVS Exams

Maths Quiz for DSSSB & KVS/NVS Exams_30.1

Q1. Three years ago, the average age of a family of 5 members was 17 yr. A baby having been born, the average age of the family is the same today. The present age of the baby is
(a) 1 yr
(b) 1 1/2 yr
(c) 2 yr
(d) 3 yr

Q2. The ratio of the ages of two persons is 4 : 7 and age of one of them is greater than that of the other by 30 yr. The sum of their ages (in years) is
(a) 110
(b) 100
(c) 70
(d) 40

Q3. The average age of two boys and their father is greater than the average age of those two boys and their mother by 3 yr. The average age of the four is 19 yr. If the average age of the two boys be 51/2 yr, then find the age of the father and the mother.
(a) 37 yr and 28 yr
(b) 47 yr and 38 yr
(c) 50 yr and 41 yr
(d) 35 yr and 32 yr

Q4. I am three times as old as my son. After 15 years, I will be twice as old as my son. The sum of our ages is
(a) 48 yr
(b) 60 yr
(c) 64 yr
(d) 72 yr

Q5. Average age of 5 boys is 16 yr and average age of 4 boys is 16 yr 3 months. The age of the 5th boys is
(a) 15 yr
(b) 15 yr 6 months
(c) 15 yr 4 months
(d) 15 yr 2 months

Q6. The average age of a family of 10 members is 20 yr. If the age of the youngest member of the family is 10 yr, then the average age of the members of the family just before the birth of the youngest members was approximately.
(a) 27.14 yr
(b) 12.5 yr
(c) 14.28 yr
(d) 11 1/9 yr

Q7. Average age of 8 men increased by 3 yr, when two of them whose ages are 30 yr and 34 yr are replaced by 2 persons. What is the average age of the 2 persons?
(a) 24 yr
(b) 32 yr
(c) 44 yr
(d) 48 yr

Q8. In a school with 600 students, the average age of the boys is 12 yr and that of the girls is 11 yr. If the average age of the total students is 11 yr and 9 months, then the number of girls in the school is
(a) 450
(b) 150
(c) 250
(d) 350

Q9. The average age of 45 persons is decreased by 1/9 yr, when one of them having 60 yr is replaced by a new comer. Then, the age of the new comer is
(a) 45 yr
(b) 55 yr
(c) 59 yr
(d) 49 yr

Q10. The average age of a husband and wife, who were married 4 yr ago, was 25 yr at the time of their marriage. The average age of the family consisting of husband, wife and a child, born during the interval is 20 yr today. The age of the child is
(a) 1 yr
(b) 2 yr
(c) 2.5 yr
(d) 3 yr
Solutions

S1. Ans.(c)
Sol. Total age of a family of 5 members, 3 yr ago = 5 × 17 = 85 yr
∴ Total present age of a family of 5 members = 85 + 5 × 3
= 85 + 15 = 100 yr
total present age of a family of 6 members = 6 × 17 = 102 yr
∴ Present age of the baby = (102 – 100) = 2 yr

S2. Ans.(a)
Sol. Let the ages of two persons be 4x and 7x respectively.
7x – 4x = 30
⇒ 3x = 30
∴ x = 10
Age of first person = 4 × 10 = 40 yr
Age of second person = 7 × 10 = 70 yr
Sum of their ages = 40 + 70 = 110 yr
Maths Quiz for DSSSB & KVS/NVS Exams_40.1
S4. Ans.(b)
Sol. Let the son’s present age be x yr.
∴ Father’s present age = 3x yr.
After 15 yr, 3x + 15 = 2 (x + 15)
⇒ 3x + 15 = 2x + 30
⇒ x = 30 – 15 = 15
∴ Sum of their present ages
= x + 3x = 4x
= 4 × 15 = 60 yr

S5. Ans.(a)
Sol. average age of 5 boys = 16 yr
Sum of ages of 5 boys = 16 × 5 = 80 yr
Average age of 4 boys = 16 yr 3 months
= 16 yr + 3/12 yr = 16 yr + 1/4 yr
Sum of ages of 4 boys
= 4 × (16 + 1/4) yr
= 64 + 1 = 65 yr
∴ Age of 5th boy
= Sum of ages of 5 boys – Sum of ages of 4 boys 
= 80 – 65 
= 15 yr

S6. Ans.(d)
Sol. Average age of 10 members = 20 yr
Sum of the present ages of 10 members 
= 20 × 10 = 200 yr
Total age of 9 members 10 yr ago
= 200 – (9 × 10 + Age of the youngest member)
= 200 – (9 × 10 + 10)
= 200 – 100 = 100 yr
∴ Average = 100/9 = 11 1/9 yr

S7. Ans.(c)
Sol. (8a +2x – 30 -34)/8 = a + 3
8a +2x -64 = 8a +24
2x =88 
= 88/2 = 44 yr

Maths Quiz for DSSSB & KVS/NVS Exams_50.1
S10. Ans.(b)
Sol. 4 yr ago, 
Average age of husband and wife = 25 yr
Sum of ages of husband and wife 4 yr ago 
= 25 × 2 = 50
Sum of present ages of both
= 50 + 8 = 58 yr
Average age of all three persons = 20
Sum of the present ages of husband, wife and child
= 3 × 20 = 60 yr
∴ Child’s present age = 60 – 58 = 2 yr