1.) Find the average of all prime numbers between 30 and 50?
A. 26.25 B. 39.8
C. 37.75 D. None of these
Answer: Option B Explanation There are five prime numbers between 30 and 50. They are 31,37,41,43 and 47. Therefore the required average= (31+37+41+43+47)/5 ==> 199/5 ==> 39.8.
2.) Find the average of first 40 natural numbers?
A. 27.5 B. 19.8
C. 20.05 D. None of these
Answer: Option C Explanation Sum of first n natural numbers=n (n+1)/2; So, Sum of 40 natural numbers= (40*41)/2 ==> 820. Therefore the required average= (820/40) ==> 20.5.
3.) Find the average of first 20 multiples of 7?
A. 22.66 B. 73.5
C. 37.75 D. None of these
Answer: Option B Explanation Required average =7(1+2+3+……. +20)/20 ==> (7*20*21)/ (20*2) ==> (147/2)=73.5.
4.) The average of four consecutive even numbers is 27. find the largest of these numbers?
A. 19 B. 27
C. 30 D. None of these
Answer: Option C Explanation Let the numbers be x, x+2, x+4 andx+6. Then, (x+(x+2)+(x+4)+(x+6))/4) = 27 ==> (4x+12)/4 = 27 ==> x+3=27 à x=24. Therefore the largest number=(x+6) =24+6=30.
5.) There are two sections A and B of a class consisting of 36 and 44 students respectively. If the average weight of section A is 40kg and that of section B is 35kg, find the average weight of the whole class?
A. 22.66 kg B. 73.5 kg
C. 37.25 kg D. None of these
Answer: Option C Explanation Total weight of(36+44) students=(36*40+44*35)kg =2980kg. Therefore weight of the total class=(2980/80)kg = 37.25kg.
