Question

Question 30 A man deposited Rs 10000 in a bank at the rate of 5% simple interest annually. Find the amount in 15th year since he deposited the amount and also calculate the total amount after 20 years.

Class X1 - Maths -Sequences and Series Page 200

Answer 1

After 1 year , Interest on 10,000 Rs
= 10000 × 5 × 1/100 [ use , SI = P × R × T/100]
= 500 Rs
So, amount in 1 year = 10,000 + 500
= 10, 500 Rs

now, interest on 10,000 for 2 years
= 10000 × 5 × 2/100
= 1000
so, amount after 2 years = 10000 + 1000
= 11,000 Rs

Similarly ,
interest on 10,000 in 3years
= 10000 × 5 × 3/100
= 1500 Rs
so, amount after 3 years = 10,000 + 1500
= 11,500 Rs

so, amount in account of man in 1st, 2nd , 3rd .. are 10,000 , 10,500 , 11000......
here,
first term ( a ) = 10,000
common difference ( d ) = 500
amount in 15th year = T₁₅ = a + (15 - 1)d
= 10,000 + (15 - 1) × 500
= 10,000 + 70,000
= 17,000 Rs

amount after 20 years = T₂₁ = a + (21 - 1)d
= 10,000 + (21 - 1) × 500
= 10,000 + 20 × 500
= 10,000 + 10,000
= 20,000 Rs