AP sumHardQuestion 210012
Question
Find the sum of all integers between 1 and 100 which are divisible by 3 or 5:
- A2317
- B2418Correct
- C2317+316
- D2633
Correct answer
2418
Explanation
Sum(÷3) + Sum(÷5) − Sum(÷15). Multiples of 3 in 1–100: 3,6,...,99, n=33, S=33×51=1683. Multiples of 5: 5,10,...,100, n=20, S=20×52.5=1050. Multiples of 15: 15,30,...,90, n=6, S=6×52.5=315. Total = 1683+1050−315 = 2418.