40. The sum of first 8 term of an AP is 100 and sum of first 19 terms

1.	40. The sum of first 8 term of an AP is 100 and sum of first 19 terms is 551. Find AP
Answer» Let a be first term and d be common difference Sum of first 8 terms (8/2)[2a+(8-1)d] = 100⇒2a + 7d =25_____(1) Sum of first 19 termsand (19/2)[2a + (19-1)d] = 551⇒2a + 18d = 58____(2) subtracting eq (1) and eq (2)11d = 33⇒d = 3 so a = (25 - 21)/2 = 2 Therefore, AP = 2, 5, 8, 11, 14.......

40. The sum of first 8 term of an AP is 100 and sum of first 19 terms is 551. Find AP

Answer»

Let a be first term and d be common difference

Sum of first 8 terms (8/2)[2a+(8-1)d] = 100⇒2a + 7d =25_____(1)

Sum of first 19 termsand (19/2)[2a + (19-1)d] = 551⇒2a + 18d = 58____(2)

subtracting eq (1) and eq (2)11d = 33⇒d = 3

so a = (25 - 21)/2 = 2

Therefore, AP = 2, 5, 8, 11, 14.......