Q10. The average age of students of a class is 15.8 years. The average age of boys in the class is 16.4 years and that of the girls is 15.4 years. The ration of the number of boys to the number of girls in the class is:
A. 1:2
B. 2:3
C. 3:4
D. 3:5
Let the ratio be k : 1. Then,
k * 16.4 + 1 * 15.4 = (k + 1) * 15.8
= (16.4 - 15.8)k = (15.8 - 15.4)
= k = 0.4/0.6 = 2/3
Required ratio = 2/3 : 1 = 2:3.
1. The average of women and child workers in a factory was 15%yr. The average age of all the 16 children was 8yr and average age of women workers was 22 yrs if ten women workers were married then the number of unmarried women workers were
A. 16
B. 12
C. 8
D. 6
Let the number of women workers be x
According to the question 22*x+16*8 = 15(16+x)
=> 22x+128 =240 +15x
=> 22x-15x = 240 -128
=> 7x=112
Therefore, x=112/7 =16
Therefore, Unmarried women workers =(16-10) =6
Q2. The mean marks of 30 students in a class is 58.5. Later on it was found that 75 was wrongly recorded as 57. Find the correct them.
A. 57.4
B. 57.5
C. 58.9
D. 59.1
Correct mean = 30x 58.5 -57 +75/30
= 1755+18/30
= 1773/30
= 59.1
Q3. A person travels from x to y at a speed of 40Km/h and returns by increasing his speed 50%. What is his average speed for both the trips?
A. 36km/h
B. 45km/h
C. 48km/h
D. 50km/h
Speed of person from x to y =40 km/h
Speed of person from y to x =(40x150)/100 = 60km/h
Since the distance travelled is same
Therefore, Average Speed = (2x40x60)/40+60 = 48km/h
Q4. The average of 18 observations was calculated and it was 124. Later on it was discovered that two observations 46 and 82 were incorrect. The correct values are 64 and 28. The correct average of 18 observations is
A. 123
B. 137
C. 121
D. 122
Sum of 18 observations = 18x124 =2232
Correct sum of 18 observations = 2232-46-82+64+28
= 2196
Therefore, Correct average =2196/18 = 122.
Q5. 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:
A. 17 kg
B. 20 kg
C. 26 kg
D. 31 kg
Let A, B, C represent their respective weights. Then, we have: A + B + C = (45 x 3) = 135 .... (i) A + B = (40 x 2) = 80 .... (ii) B + C = (43 x 2) = 86 ....(iii) Adding (ii) and (iii), we get: A + 2B + C = 166 .... (iv) Subtracting (i) from (iv), we get : B = 31. B's weight = 31 kg.
Q6. The average weight of 16 boys in a class is 50.25 kg and that of the remaining 8 boys is 45.15 kg. Find the average weights of all the boys in the class.
A. 47.55 kg
B. 48 kg
C. 48.55 kg
D. 49.25 kg
NO Solution
Q7. The arithmetic mean of the scores of a group of students in a test was 52. The brightest 20% of them secured a mean score of 80 and the dullest 25% a mean score of 31. The mean score of remaining 55% is:
A. 45
B. 50
C. 51.4 approx.
D. 54.6 approx.
Let the required means score be x. Then,
20 * 80 + 25 * 31 + 55 * x = 52 * 100
= 1600 + 775 + 55x = 5200
= 55x = 2825
= x = 565/11 = 51.4.
Q8. The average salary of all the workers in a workshop is Rs. 8000. The average salary of 7 technicians is Rs. 12000 and the average salary of the rest is Rs. 6000. The total number of workers in the workshop is:
A. 20
B. 21
C. 22
D. 23
Let the total number of workers be x. Then,
8000x = (12000 * 7) + 6000(x - 7)
= 2000x = 42000
= x = 21.
Q9. In an examination a pupil's average marks were 63 per paper. If he had obtained 20 more marks for his Geography paper and 2 more marks for his History paper, his average per paper would have been 65. How many papers were there in the examination?
A. 8
B. 9
C. 10
D. 11
Let the number of papers be x. Then,
63x + 20 + 2 = 65x
= 2x = 22
= x = 11.