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 = $\left(\frac{2ab}{a+b}\right)$
21.The average age of the boys in a class is 16 years and that of the girls is 15 years. The average age for the whole class is : A) 10 years B) 15.5 years C) 16 years D) Data inadequate View Answer Report DiscussAnswer: Option DExplanation:Clearly to find the average we ought to know the number of boys ,girls or students in the class ,neither of which has been given .So,the data provided is inadequate.
22.The average of five consecutive odd numbers is 61. What is the difference between the highest and lowest numbers ? A) 2 B) 5 C) 8 D) Cannot be determined E) None of these View Answer Report DiscussAnswer: Option CExplanation:Let the number be x,x+2,x+4,x+6 and x+8then $\frac{x+(x+2)+(x+4)+(x+6)+(x+8)}{5}=61$5x+20=805x=57So required difference = (57+8)-57=8
23.The average of 7 consecutive numbers is 20. The largest of these numbers is : A) 20 B) 22 C) 23 D) 24 View Answer Report DiscussAnswer: Option CExplanation:Let the numbers be x,x+1,x+2,x+3,x+4,x+5,x+6Average = $\frac{x+(x+1)+(x+2)+(x+3)+(x+4)+(x+5)+(x+6)}{7}=20$7x+21 = 140x= $\frac{140-21}{7}$x=17Latest number is x+6= 23
24.The average of all odd numbers upto 100 is : A) 49 B) 49.5 C) 50 D) 51 View Answer Report DiscussAnswer: Option CExplanation:Sum odf odd numbers upto 100 = 1+3+5+7+....+95+97+9 =(1+99)+(3+97)+(5+95)+.....+upto 25 pairs = 100+100+100+...+(25 times)=2500Avergae = 2500/50=50
25.The average of the two-digit numbers, which remain the same when the digits interchange their positions, is : A) 33 B) 44 C) 55 D) 66 View Answer Report DiscussAnswer: Option CExplanation:Average = $\frac{11+22+33+44+55+66+77+88+99}{9}$$=\frac{(11+99)+(22+88)+(33+77)+(44+66)+55}{9}$$=\frac{4\times110+55}{9}=\frac{495}{9}=55$
