Average - General QuestionsAverage - Important Formulas and Facts 1) Average = Sum of observations / Number of observations 2) Suppose an object covers a certain distance at 'a' kmph and an equal distance at 'b' kmph. Then the average speed during the whole journey = $\left(\frac{2ab}{a+b}\right)$
1.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 ratio 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 View Answer Report DiscussAnswer: Option BExplanation:Let ratio be k:1 then kx16.4 =1x15.4 =(k+1)x15.8=> (16.4-15.8)k =(15.8-15.4)=> $k=\frac{0.4}{0.6}=\frac{2}{3}$required ratio = $\frac{2}{3}:1=2:3$
2.In a school with 600 students, the average age of the, boys is 12 years and that of the girls is 11 years.- If the average age of the school is 11 years 9 months, then the number of girls in the school is : A) 150 B) 250 C) 350 D) 450 View Answer Report DiscussAnswer: Option AExplanation:Let the number of girls be x.Number of boys be 600-x $11\frac{3}{4}\times600=11x+12(600-x)=>x=7200-7050=>x=150$
3.A certain factory employed 600 men and 400 women and the average wage was Rs. 25.50 per day. If a woman got Rs. 5 less than a man, then what are their daily wages ? A) Man : Rs. 25; Woman : Rs. 20 B) Man • Rs. 27.50, Woman : Rs. 22.50 C) Man : Rs. 30, Woman : Rs. 25 D) Man : Rs. 32.50, Woman : Rs. 27.50 View Answer Report DiscussAnswer: Option BExplanation:Let the daily wage of a man is xDaily wage of a woman is x-5Now 600x+400(x-5)=25.50*(600+400)=>1000x=27500=>x=27.50So man wage is 27.5 and woman's wage is x-5=27.50-5=22.50
4.After replacing an old member by a new member, it was found that the average age of five members of a'club is the safrie as it was 3 years ago. What is the difference between the ages of the replaced and the new member ? A) 2 years B) 4 years C) 8 years D) 15 years View Answer Report DiscussAnswer: Option DExplanation:Age decreased = (5x3)years =15 yearsSo the requied difference = 15 years
5.The average age of husband, wife and their child 3 years ago was 27 years and that of wife and the child 5 years ago was 20 years. The present age of the husband is : A) 35 years B) 40 years C) 50 years D) None of these View Answer Report DiscussAnswer: Option BExplanation:Sum of the present ages of husband ,wife and child =27x3+3x3 years = 90 years Sum of the present ages of wife and child =20x2+5x2 years = 50 yearsTherefore husband's present age = 90-50 years = 40 years
