| Find the sum of all positive multiples of 3 less than 50. [SSC (CGL) Mains 2014] |
A) 400
B) 404
C) 408
D) 412
Correct Answer: C
Solution :
| Multiples of 3 up to 50 are 3, 6, 9,12,..., 42, 45, 48 |
| The terms form an AP consisting 16 terms. |
| \[\therefore \] Sum of \[AP=\frac{n}{2}(a+l)\] |
| Here, \[n=16,\]\[a=3,\]\[l=48\] |
| \[\Rightarrow \] Sum of AP\[=\frac{16}{2}(3+48)=8\times 51=408\] |
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