## Aptitude question and answer on Average

 17 The average salary per month of 30 employees in INFINITY LTD. is Rs. 4000.If the manager's salary is added, the average salary increases to Rs. 4300, What is the salary of the manager ? A.    Rs. 13500 B.    Rs. 12500 C.    Rs. 12300 D.    Rs. 13300 Answer : D.  Rs. 13300 Explanation: Salary of the manager = Rs.$(31 \times4300-30\times4000)$                                 =Rs.13300. Discuss 18 Find the average of all prime numbers between 30 and 50? A.    60.8 B.    59.8 C.    49.8 D.    39.8 Answer : D.  39.8 Explanation: There are five prime numbers between 30 and 50. They are 31,37,41,43 and 47. Therefore the required average=$(31+37+41+43+47) \over5$ => $199 \over 5$ => 39.8   Discuss 19 find the average of first 40 natural numbers? A.    20.5 B.    21.6 C.    26.8 D.    20.9 Answer : A.  20.5 Explanation: sum  of first n natural numbers=$n(n+1) \over2$ So,sum of 40 natural numbers=$(40 \times41) \over 2$= 820. Therefore  the required average=${820 \over 40}$=20.5.   Discuss 20 find the average of first 20 multiples of 7 ? A.    63.15 B.    73.5 C.    63.5 D.    83.5 Answer : B.   73.5 Explanation: Required average =$7(1+2+3+...........+20) \over20$ By usingh below formula $1 + 2 + 3 + \cdots + n=\sum{n}= \dfrac{n(n+1)}{2}$ We will get  => $(7 \times20 \times21) \over20 \times2$=$147 \over 2$= 73.5. Discuss 21 The average of four consecutive even numbers is 27. find the largest of these numbers ? A.    30 B.    31 C.    32 D.    33 Answer : A.  30 Explanation: Let the numbers be $x,x+2,x+4$ and $x+6.$ then, ${(x+(x+2)+(x+4)+(x+6)) \over4 }= 27$  $=> {(4x+12) \over4 } = 27$ $x+3=27$ $x=24.$ Therefore the largest number=(x+6)=24+6=30.   Discuss 22 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.    35.25 kg B.    36.25 kg C.    37.25 kg D.    38.25kg Answer : C.  37.25 kg Explanation: Total weight of (36+44) students=$(36 \times40+44 \times35)kg$  =2980kg. Therefore average weight of the whole class=$2980 \over80$kg  =37.25kg.   Discuss 23 Nine persons went to a hotel for taking their meals 8 of them spent Rs.12 each on their meals and the ninth spent Rs.8 more than the average expenditure of all the nine.What was the total money spent by them ? A.    116 B.    117 C.    118 D.    119 Answer : B.   117 Explanation: Let the average expenditure of all nine be Rs.x Then $12 \times8+(x+8)=9x$ or   $8x=104$ or $x=13$. Total money spent = 9x=Rs. $9 \times 13$=Rs.117.   Discuss 24 Of the three numbers, second is twice the first and is also thrice the third.If the average of the three numbers is 44.Find the largest number. A.    70 B.    71 C.    72 D.    73 Answer : C.  72 Explanation: Let the third number be x. Then second number = 3x. First number=$3x \over2$. Therefore $x+3x+ \bigg({3x \over2 } \bigg)$=$(44 \times3)$ or x=24 So largest number= 2nd number=3x=72.   Discuss