#### Question

Find the sum of all numbers between 200 and 400 which are divisible by 7.

#### Solution

The numbers lying between 200 and 400, which are divisible by 7, are

203, 210, 217, … 399

∴First term, *a* = 203

Last term, *l* = 399

Common difference, *d* = 7

Let the number of terms of the A.P. be *n*.

∴ *a*_{n} = 399 = *a* + (*n* –1) *d*

⇒ 399 = 203 + (*n* –1) 7

⇒ 7 (*n* –1) = 196

⇒ *n* –1 = 28

⇒ *n* = 29

Is there an error in this question or solution?

Solution Find the Sum of All Numbers Between 200 and 400 Which Are Divisible by 7. Concept: Arithmetic Progression (A.P.).