Question: At a certain rate of simple interest Rs. 800 amounted to Rs. 920 in 3
years. If the rate of interest be increased by 3%, what will be the amount
after 3 years? [साधारण ब्याज की एक विशेष दर से 3 वर्षों में 800 रूपये बढ़कर 920
रूपये हो जाता है. यदि ब्याज की दर में 3% की वृद्धि होती है, तो बताएं कि 3
वर्षों के बाद मिश्रधन कितना हो जायेगा?] [Ans. (b) Rs. 992]
(a) Rs. 929 (b) Rs. 992 (c) Rs. 892
(d) Rs. 982 (e) None of these
Detailed
Explanation: Since principal and time remain the same, and only rate is
increased by 3%, so at the rate of 3%
pan and for the period of 3 years; the extra interest generated (3% × 3 = 9%)
only is to be paid in addition to the amount (Rs. 920) paid earlier. There is no need to calculate
the rate of interest.
Principal
is always taken as 100% and simple interest is calculated on the basis of
principal (assuming it as 100% always) not on the basis of amount.
First
Method:
100% ≡? = Rs. 800
9% ≡?
= Rs. 72
Required
Amount = Rs. (920 + 72) = Rs. 992 Ans.
Second
Method:
9% of Rs. 800 = Rs. 72
Required
Amount = Rs. (920 + 72) = Rs. 992 Ans.
Third
Method: Rs. 800 becomes in Rs. 920 in 3 years, so the simple interest in 3
years is Rs. 120. The simple interest in one year is Rs. 40, which is 5% of Rs.
800 (As 100% ≡ Rs. 800, or it means 10% ≡ Rs. 80, or it means 5% ≡ Rs. 40). If
the rate of interest is increased by 3%, then the new increased rate of
interest is 8% pan. In three years, the S.I. (Simple Interest) will be 24%
100% ≡ Rs. 800
25% ≡ Rs. 200
1% ≡
Rs. 8
So, 24% ≡ Rs. 192
Required
Amount = Rs. (920 + 72) = Rs. 992 Ans.
Or,
we can proceed as
100% ≡ Rs. 800
20% ≡ Rs. 160 (since, 10% ≡ Rs. 80)
4% ≡
Rs. 32 (since,
1% ≡ Rs. 8)
So, 24%
≡ Rs. 192
Required Amount = Rs. (920
+ 72) = Rs. 992 Ans.
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