Question

How many terms of an A.P 1, 4, 7,………….are needed to make the sum 715

Answer 1

$<b> <tt>$
GIVEN:

a= 1 , d= a2-a1 = 4-1=3 and last term or An =715.

we know the formula =>

An = a + ( n - 1 ) × d .

=> 715 = 1 + ( n - 1 ) × 3

=> 715 = 1 + 3n - 3

=> 715 = 3n -2

=> 2+715 = 3n

=> 3n = 717

=> n = 717/3

=> n = 239 .