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Arithmetic Progressions

Question
CBSEENMA10007980

A sum of Rs. 1000 is invested at 8% simple interest per year. Calculate the interest at the end of each year. Do these, interests form an A .P. ? If so, find the interest at the end of 30 yrs.

Solution

Here,  P = 1000,  r = 8%
Interest at the end of first year.
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Interest at the end of second year
      equals fraction numerator straight P cross times straight r cross times straight t over denominator 100 end fraction
equals space fraction numerator 1000 cross times 8 cross times 2 over denominator 100 end fraction equals R s. space 160
Interest at the end of third year
equals fraction numerator straight P cross times straight r cross times straight t over denominator 100 end fraction
equals fraction numerator 1000 cross times 8 cross times 3 over denominator 100 end fraction equals space Rs. space 240
So, we have 80, 160, 240, ..............
Here, a = 80, d = 80
Therefore, interest at the end of 30 yrs. i.e. a30 is,
a30 = a + (30 –1) d = 80 + 29 x 80
= 80 + 2320 = 2400
So the interest at the end of 30 years is Rs. 2400.