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Q1(iv):
In which of the following situations, does the list of numbers involved make an arithmetic progression, and why? (iv) The amount of money in the account every year, when ₹ 10000 is deposited at compound interest at 8 % per annum.

Solution :

Given:

Principal amount ($P$) = ₹ $10000$

Rate of interest ($r$) = $8\%$ per annum

The interest is compounded annually.

To Find:

Whether the sequence of amounts at the end of each year forms an Arithmetic Progression (AP).

Step 1: Understanding the Formula for Compound Interest

The amount ($A$) after $n$ years with compound interest is given by the formula:

$A = P \left(1 + \frac{r}{100}\right)^n$

Where:

  • $P = 10000$
  • $r = 8$
  • $n$ is the number of years ($n = 1, 2, 3, \dots$)

Step 2: Calculating the amount for consecutive years

Let $a_1, a_2, a_3, \dots$ be the amount in the account at the end of the 1st, 2nd, and 3rd year respectively.

For $n = 1$ (Amount at the end of 1st year):

$a_1 = 10000 \left(1 + \frac{8}{100}\right)^1 = 10000(1.08) = 10800$

For $n = 2$ (Amount at the end of 2nd year):

$a_2 = 10000 \left(1 + \frac{8}{100}\right)^2 = 10000(1.08)^2 = 10000(1.1664) = 11664$

For $n = 3$ (Amount at the end of 3rd year):

$a_3 = 10000 \left(1 + \frac{8}{100}\right)^3 = 10000(1.259712) = 12597.12$

Step 3: Checking for Arithmetic Progression

A sequence is an Arithmetic Progression if the difference between consecutive terms is constant (i.e., $a_{n+1} - a_n = d$, where $d$ is the common difference).

Calculate the first difference ($d_1$):

$d_1 = a_2 - a_1 = 11664 - 10800 = 864$

Calculate the second difference ($d_2$):

$d_2 = a_3 - a_2 = 12597.12 - 11664 = 933.12$

Step 4: Conclusion

Since $d_1 \neq d_2$ ($864 \neq 933.12$), the difference between consecutive terms is not constant.

[By definition, a sequence is an AP if and only if the common difference is constant for all terms.]

Final Answer: The list of numbers does not form an Arithmetic Progression because the difference between consecutive terms is not constant.


More Questions from Class 10 Mathematics Arithmetic Progression EXERCISE 5.1


CBSE Solutions for Class 10 Mathematics Arithmetic Progression


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