Question

Find the sum of all the natural number:
a) between 50 and 500 which is divisible by 3 and 5.

Answer 1

Answer: 8325

Step-by-step explanation:

A Number that is divisible by 3 and 5 Implies that it must be divisible by 15.

Least and Greatest Number That is Divisible by 15 Between 50 are 60 and 495 Respectively.

So The Given Sum is

S = 60 + 75 + 90 + ..... + 495

tn = a + (n-1)d

495 = 60 + (n-1)*15

(n-1)*15 = 435

n-1 = 495/15

n = 1 + 29

n = 30

Sn = (n/2)(a+L) Where , (L = 495 , a = 60)

Sn = 15(60+495)

Sn = 15*555

Sn=8325