| The average age of group of persons going for picnic is 16 yr. Twenty new persons with an average age of 15 yr join the group on the spot due to which their average become 15.5 yr. Find the number of persons initially going for picnic. |
A) 5
B) 20
C) 25
D) 30
Correct Answer: B
Solution :
| Let the number of persons initially going to picnic be x. |
| Now, average\[=\frac{x\times 16+20\times 15}{x+20}\] |
| \[\Rightarrow \]\[15.5\times (x+20)=16x+300\] |
| \[\Rightarrow \]\[15.5x+310=16x+300\] |
| \[\Rightarrow \]\[0.5x=10\]\[\Rightarrow \]\[x=20\] |
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