Question

Rina has a cumulative deposit account of Rs 400 per month at 10% p.a simple interest. If she get!
Rs 30100 at the time of maturity, find the total time for which the account was held.
(5)​

Answer 1

Let say account was held  for  n moths

1st Deposit got interest for n months

2nd deposit got for n - 1 months

and last Deposit nth for 1 month

Interest for n months = 400 * (n/12) * 10/100  = 40n/12  = 10n/3

10n/3 , 10(n-1)/3 .............................................+ 10/3

400n is deposited anount  & interest

Sum = 400n  +  (n/2)(10n/3  + 10/3)

= 400n  + 5n²/3  + 5n/3

400n  + 5n²/3  + 5n/3 = 30100

=> 5n² + 1200n + 5n = 90300

=> n² + 241n - 18060 = 0

=> n²  + 301n - 60n - 18060 = 0

=> (n + 301)(n - 60)  =0

=> n = 60

Account was held for 60 months = 5 years

Answer 2

Step-by-step explanation:

$Interest = P*n(n+1)r \div 12 \times 100 \times 2$

$Maturity \: Value = Interest + Account \: deposited$