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17.

The average weight of girls in a class of 50 students is 40 kg. Which of the following could be the average weight of the entire class if the average weight of 30 of the boys is 50 kg?
(a)42 kg
(b)43 kg
(c)45 kg
(d)47 kg
Answer is: DIf there are exactly 30 boys, the average weight of the entire class is obtained from the rule of allegation table as follows.
No. of girls = 20
Average weight of girls = 40
No. of boys = 30
Average weight of boys = 50
⇒ (50 - X)/(X - 40) = 20/30
⇒ 150 - 3X = 2X - 80
⇒ X = 230/5 = 46
As, there are possibly more boys, the average could be greater than 46 but not less.

18.

The average marks scored by girls in a class of 40 students in an examination is 80. If the number of boys in the class and their average marks in the same examination are 25 and 72 respectively, what are the average marks of all the students in the class?
(a)74
(b)75
(c)76
(d)78
Answer is: BTotal number of students = 40
Number of boys = 25
Number of girls = 40 - 25 = 15
Average marks for the entire class = [25 x 72 + 15 x 80]/40 = 75

19.

The average marks scored by Suresh in 5 out of six subjects in an examination is 54. To get an average of 60 in six subjects together, what is the score that Suresh must get in the sixth subject?
(a)66
(b)65
(c)90
(d)84
Answer is: CTotal marks of 5 subjects at an average of 54 is 5 x 54 = 270
Total marks 6 subjects at an average of 60 is 6 x 60 = 360
∴ In the sixth subject 360 - 270 = 90 marks are to be scored by Suresh.

20.

The ratio of the number of girls to that of boys is 2 : 3. If the average weight of girls is 35 kg and that of boys is 40 kg, what is the average weight of the entire class?
(a)36
(b)37
(c)38
(d)39
Answer is: CLet the number of girls be 2X, the number of boys is 3X.
∴ Average weight of the class = [(2X x 35) + (3X x 40)]/(2X + 3X)
∴ Average weight of the class = (70X + 120X)/5X = 190X/5X = 38 kg.

21.

The average number of chocolates with four children is 4. Another child joins them. Now, the average number of chocolates with the five children is 5. What is the number of chocolates with the fifth child?
(a)1
(b)9
(c)5
(d)6
Answer is: BTotal number of chocolates possessed by four children = 4 x 4 = 16
Total number of chocolates with five children together, after fifth child joined = 5 x 5 = 25
∴ The number of chocolates with the fifth child = number of chocolates increased = 25 - 16 = 9.

22.

A bag contains 2 kg of potatoes and 3 kg of tomatoes. If the cost of potatoes is Rs 5 per kg and that of tomatoes is Rs 8 per kg, then what is the average price per kilogram of the vegetables in the bag?
(a)Rs 6
(b)Rs 6.60
(c)Rs 6.80
(d)Rs 7
Answer is: CTotal cost of potatoes = 2 x 5 = Rs. 10
Total cost of tomatoes = 3 x 8 = Rs. 24
Total cost of the vegetables in the = 10 + 24 = Rs. 34
Average cost per kg of vegetables in the bag = 34/5 = Rs 6.80

23.

The average of earnings of a man for the first four months, the fifth to the eighth months and the last four months in a particular year are Rs 5000 per month, Rs 6000 per months and Rs 10000 per months respectively. What is the average salary per month in that year?
(a)6000
(b)7000
(c)8000
(d)9000
Answer is: BAs the period for which each of these average salaries is drawn is the same i.e. four months, the average of these salaries will give the average salary for the entire year.
∴ The average salary per month = (5000 + 6000 + 10000)/3
∴ The average salary per month = 21000/3 = Rs 7000 per months.

24.

The average income per person for a family of 5 members is Rs 8000 per month. In a particular month, every member got Rs 800 less than the usual. What is the average income per person for that month?
(a)Rs 4000
(b)Rs 7200
(c)Rs 6000
(d)Rs 6400
Answer is: BTotal income for the family = 5 X 8000 = Rs 40000
In a particular month a total 800 x 5 = 4000 is decreased
Total income in that month = 40000 - 4000 = 36000
Average income per person = 36000/5 = Rs 7200

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