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11. The average age of students in section A of 50 students is 14 years and the average age of students in section B of 30 students is 6 years. Find the average age of students in both sections taken together.
  A.  11 yrs
  B.  14 yrs
  C.  10 yrs
  D.  8 yrs
     
   
View Answer

Shortcut: If the average of 'l' boys is 'y' and the average of 'm' boys is 'z' then the average of all of them put together is
ly + mz / l + m
Here, l = 50, y = 14, m = 30, z = 6 Putting these values in shortcut, we get Average =
50x14 + 30x6 / 50 + 30
= 11 years

12. A man bought 13 shirts of Rs 50 each, 15 pants of Rs 60 each and 12 pairs of shoes at Rs 65 a pair. Find the average value of each article.
  A.  Rs 62.25
  B.  Rs 58.25
  C.  Rs 55.75
  D.  Rs 52.25
     
   
View Answer

Using the shortcut, Average =
l1y1 + l2y2 + l3y3 + ....... + lnyn / l1 + l2 + l3 + ....... + ln
Average =
13x50 + 15x60 + 12x65 / 13+15+12
= Rs 58.25

13. The average score of a cricketer in two matches is 27 and in three other matches is 32. Then find the average score in all the five matches.
  A.  32
  B.  27
  C.  30
  D.  33
     
   
View Answer

Average of 5 matches =
2x27 + 3x32 / 2 + 3
=
54 + 96 / 5
= 30

14. The average age of 600 scholars of a school is 10.75 years. By the enrolment of 40 new scholars the average is reduced to 10.4375 years. Find the average age of the new scholars.
  A.  3
4 / 5
yrs
  B.  4
5 / 3
yrs
  C.  5
3 / 4
yrs
  D.  5
4 / 3
yrs
     
   
View Answer

Let the average age of the new scholars be y. Now,
600x10.75+40xy / 600 + 40
= 10.4375 or, 6450+40y=6680 or, y=
23 / 4
= 5
3 / 4

15. In a cerain primary school, there are 60 boys of age 12 each, 40 of age 13 each, 50 of age 14 each and 50 of age 15 each. The average age (in years) of the boys of the school is:
  A.  13.45
  B.  15.75
  C.  11.25
  D.  19.45
     
   
View Answer

Let the average age of the new scholars be y. Now,
60 x 12 + 40 x 13 + 50 x 14 + 50 x 15 / 60 + 40 + 50 + 50
=
2690 / 200
= 13.45

16. The average height of 30 girls out of a class of 40 is 160cm and that of the remaining girls is 156cm. The average height of the whole class is:
  A.  155cm
  B.  148cm
  C.  162cm
  D.  159cm
     
   
View Answer

Let the average age of the new scholars be y. Now,
30x160+10x156 / 30 + 10
=
23 / 40
=
4800+1560 / 40
=
6360 / 40
= 159 Hence, average of whole class is 159 cm.

17. The average height of 30 boys out of a class of 50, is 160 cm. If the average height of the remaining boys is 165 cm, the averge height of the whole class (in cm) is:
  A.  162
  B.  165
  C.  155
  D.  158
     
   
View Answer

Using the shortcut, we get Average =
30x160 + 20x165 / 30 + 20
=
4800 + 3300 / 30 + 20
=
8100 / 50
= 162

18. The average of 10 quantities is 12. The average of 6 of them is 8. What is the average of remaining four numbers.
  A.  18
  B.  24
  C.  14
  D.  20
     
   
View Answer

Shortcut: If the average of 'l' boys is 'y' and the average age of 'm' boys out of them (l boys) is 'z' then the average of rest of the boys is
ly - mz / l - m
Here, l = 10, y = 12, m = 6, z = 8 Putting these values in shortcut, we get Average of remaining 4 numbers =
10x12 - 6x8 / 10 - 6
= 18

19. The average age of 30 students in a class is 12 years. The average age of a group of 5 of the students is 10 years and that of another group of 5 students is 14 years. Find the average age of the remaining studetns.
  A.  16 years
  B.  12 years
  C.  8 years
  D.  10 years
     
   
View Answer

Using shortcut, we get Average of remaining students =
30x12 - {(5x10)+(5x14)} / 30 -(5+5)
=
240 / 20
= 12

20. 30 horses are bought for Rs 150000. The average cost of 18 of them is Rs 4500. What is the average cost of others?
  A.  Rs 5550
  B.  Rs 5950
  C.  Rs 6050
  D.  Rs 5750
     
   
View Answer

Using shortcut, we get Average of remaining students =
150000(30x5000) - 18x4500 / 30 - 18
= Rs 5750

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