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The average of n observations is 40. If one observation of value 80 is added, then the average of all the observations is 41. What is the value of n?
The Average of n observation = 40
total of n observation = 40 n
on adding 80, total becomes = 40n + 80 and number of observation = n +1
Now average = 41
so according to question $$\dfrac {40n + 80}{n+1} = 41 $$
$$\Rightarrow 40n + 80 = 41 (n+1)$$
$$\Rightarrow 41n - 40 n = 80-41 $$
$$\Rightarrow n = 39 $$Ans
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