Question

find the sum ofall natural numbers between 1 to 200 which arw multiples of 5​

Answer 1

AP = 5, 10, 15 ............ 200

A= 5

D= 5

An = 200

An = A+ ( n - 1) d

200= 5 + ( n - 1) 5

200 - 5 = (n - 1) 5

195 = n - 1 5

195/5 =n -1

39 = n - 1

39+1 =n

40= n

Answer 2

a = 5

l = 200

d = 5


l = a + (n-1)d

200= 5 + (n-1)5

200 - 5 = (n - 1)5

195/5 = (n-1)

(n-1) = 39

n = 39 + 1

n = 40


S = n/2 (a + l)

S = 40/2 (5 + 200)

S = 20 (205)

S = 4100