Question

subha rao started work in 1995 at an annual salary of 5000 and received an increment of 100 each year. in which year did his income reach 7000
here in this question they used nth term formula but why they didn't use sum of n terms formula

Answer 1

Answer:

21 years

Step-by-step explanation:

Given that he started in 1995 with an initial salary of 5000 and received increment of 100 each year.

It can be observed that incomes obtained by subba rao obtained in various years are in A.P every year, his salary is increased by 100.

Hence, the salaries of each year after 1995 are 5000, 5100,5200...

Here, a = 5000, d = 100, sn = 7000

Since, tn = a + (n - 1) * d

⇒ 7000 = 5000 + (n - 1) * 100

⇒ 7000 = 5000 + 100n - 100

⇒ 7000 = 100n + 4900

⇒ 2100 = 100n

⇒ n = 21.

Therefore, after 21 years his income become 7000.

Hope it helps!