Question

Find the sum of all positive integer less than 200 that are divisible by 3 but not by 7

Answer 1

Answer:

Step-by-step explanation:

first no. divisible by 3 = 3

last number= 198

so, AP:- 3 , 6, 9, .. ..... ... . ,198

as, An = a +(n-1)d

and here d = 6-3

d = 3

so, An = 3 +(n-1) 3

198 =3 +(n-1)3

198-3 = (n-1)3

195 / 3 = n-1

65 +1 = n

66 = n..

now, S66 = n/2 (a +An)

S66 = 66/2 (3+198)

S66 = 33 * 201

S66 = 6633

Mahesh phad

Answer 2

Answer:

first no. divisible by 3 = 3

last number= 198

so, AP:- 3 , 6, 9, .. ..... ... . ,198

as, An = a +(n-1)d

and here d = 6-3

d = 3

so, An = 3 +(n-1) 3

198 =3 +(n-1)3

198-3 = (n-1)3

195 / 3 = n-1

65 +1 = n

66 = n..

now, S66 = n/2 (a +An)

S66 = 66/2 (3+198)

S66 = 33 ×201

S66 = 6633

no. divsible by 7

first no divisible by 7 is 7

common difference is 7

last number divisible by 7 is 196

an = a + (n - 1)d

196 = 7 + (n - 1)7

189= (n - 1)7

27 = (n - 1)

n = 28

S28 = 14 (2a +27d)

      = 14 ( 14 +189)

      = 14 ×203

      = 2842

S66 --  S28 = 6633 -- 2842

                   = 3791

3791 is correct answer

Step-by-step explanation: