Question

Find the sum of integers between 200 and 300 that are divisible by 13

Answer 1

First after 200 which is divisible by 13 = 208 (a)

2 term = 221

the difference = 221-208 = 13 (d)

Last term which is before 300 = 299 (aₓ)

A.P = aₓ = a+(n-1)d

299 = 208+(n-1)13

91 = (n-1)13

7 = n-1

8 = n

So now the sum of the 8 terms:

Sₓ = n/2 (a+aₓ)

S₈ = 8/2 (208+299)

= 4*507

=2028

Answer 2

Answer:

First after 200 which is divisible by 13 = 208 (a)

2 term = 221

the difference = 221-208 = 13 (d)

Last term which is before 300 = 299 (aₓ)

A.P = aₓ = a+(n-1)d

299 = 208+(n-1)13

91 = (n-1)13

7 = n-1

8 = n

So now the sum of the 8 terms:

Sₓ = n/2 (a+aₓ)

S₈ = 8/2 (208+299)

= 4*507

=2028

Step-by-step explanation: