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 = $\left(\frac{2ab}{a+b}\right)$
26.If the mean of 5 observations x, x + 2, x + 4, x + 6 and x + 8 is 11, then the mean of the last three observations is : A) 11 B) 13 C) 15 D) 17 View Answer Report DiscussAnswer: Option BExplanation:We have $[\frac{x+(x+2)+(x+4)+(x+6)+(x+8)}{5}]=11$5x+20 = 55x= 7So the numbers are 7,9,11,13,15Required mean = $\frac{11+13+15}{3}=\frac{39}{3}=13$
27.The average of 2, 7, 6 and x is 5 and the average of 18, 1, 6, x and y is 10. What is the value of y ? A) 5 B) 10 C) 20 D) 30 View Answer Report DiscussAnswer: Option CExplanation:we have : $\frac{2+7+6+x}{4}=5$ 15+x= 20x=5 Also $\frac{18+1+6+x+y}{5}=10$25+5+y=50y=20
28.A student was asked to find the arithmetic mean of the numbers 3, 11, 7, 9, 15, 13, 8, 19, 17, 21, 14 and x. He found the mean to be 12. What should be the number in place of x ? A) 3 B) 7 C) 17 D) 31 View Answer Report DiscussAnswer: Option BExplanation:we have : $\frac{3+11+7+9+15+13+8+19+17+21+14+x}{12}=12$ 137+x=144x=144-137=7
29.Find the average of all the numbers between 6 and 34 which are divisible by 5. A) 18 B) 20 C) 24 D) 30 View Answer Report DiscussAnswer: Option BExplanation:Average= $\frac{10+15+20+25+30}{5}=\frac{100}{5}=20$
30.The average of first five multiples of 3 is : A) 3 B) 9 C) 12 D) 15 View Answer Report DiscussAnswer: Option BExplanation:Average= $\frac{3(1+2+3+4+5)}{5}=\frac{45}{5}=9$
