| Out of four numbers, the average of the first three is 16 and that of the last three is 15. If the last number is 20, then the first number is |
A) 25
B) 21
C) 23
D) 28
Correct Answer: C
Solution :
| Let the four number be a, b, c and d. |
| Given, \[\frac{a+b+c}{3}=16\] i.e. \[a+b+c=48\] |
| \[\Rightarrow \]\[\frac{b+c+d}{3}=15\]\[\Rightarrow \]\[b+c+d=45\] |
| But last number, d = 20 |
| \[b+c+20=45\]\[\Rightarrow \]\[b+c=25\] |
| \[\therefore \] \[a=48-25\]\[\Rightarrow \]\[a=23\] |
| So, first number is 23. |
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