Question

if first and last term of an AP are 17 and 350 respectively. if the common difference is 9, how many terms are there and what is their sum

Answer 1

Heya !!



First term ( A ) = 17



And,


Common difference ( D ) = 9




Last term ( Tn ) = 350





A + ( N - 1 ) × D = 350




17 + ( N - 1 ) × 9 = 350



17 + 9N - 9 = 350



9N + 8 = 350



9N = 350-8



N = 38


Number of terms = 38.




Sn = N/2 × [ 2A + ( N - 1 ) × D ]



S38 = 38/2 × [ 2 × 17 + ( 38 - 1 ) × 9 ]






=> 19 ( 34 + 333 )



=> 19 × 367



=> 6973.

Answer 2

Hey!!

_________________

First term ( A ) = 17

Common Difference ( D ) = 9

Last term = 350

A + ( N - 1 ) × D = 350

=> 17 + ( N - 1 ) × 9 = 350

=> 17 + 9N - 9 = 350

=> 8 + 9N = 350

=> 9N = 350 - 8

=> 9N = 342

=> N = 342 / 9

=> N = 38

Number of terms = 38

Sn = N / 2 [ 2A + ( N - 1 ) × D ]

S38 = 38 / 2 [ 2 ( 17 ) + ( 38 - 1 ) × 9 ]

=> 34 [ 34 + 333 ]

=> 34 × 367

=> 12478 >>>>> Answer

______________________


Hope it will helps you ✌