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6.AVERAGE
Ex.1:Find the average of all prime numbers between 30 and 50?
Sol:
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.
Ex.2. find the average of first 40 natural numbers?
Sol:
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.
Ex.3. find the average of first 20 multiples of 7?
Sol:
Required average =7(1+2+3+…….+20)/20
(7*20*21)/(20*2)
(147/2)=73.5.
Ex.4. the average of four consecutive even numbers is 27. find the largest of these
numbers?
Sol:
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
x=24.
Therefore the largest number=(x+6)=24+6=30.
Ex.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?
Sol:
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 Spring '11
 vinh

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