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Mathematics · Arithmetic Progressions · NCERT Examples

Example 9

A complete, independently verified solution for NCERT Example 9.

Mathematics · Chapter 5 · NCERT Examples

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NCERT Example

Example 9

application · nth term

₹1000 is invested at 8% simple interest yearly. Do yearly accumulated interests form an AP, and what is the interest after 30 years?

Solution

Board-exam working:

an=a+(n−1)da_n=a+(n-1)d

Simple interest for one year is PR/100=1000×8/100=₹80.

Therefore the accumulated interests are ₹80,₹160,₹240,… and each consecutive difference is ₹80, so they form an AP with a=80,d=80.

For 30 years, a₃₀=80+(30−1)80=80+29×80=80+2320=₹2400.

Check directly: PRT/100=1000×8×30/100=₹2400.

Final answer

Yes; d=₹80 and the 30-year interest is ₹2400.