Simple Interest - 02

Question:  Two equal amount of money are deposited in two banks each at 5% per annum for 3 and 4 years respectively. If the difference between their interests is Rs. 42, find each sum.          

(a) Rs. 210        (b) Rs. 280      (c) Rs. 750      (d) Rs. 840     (e) none of these

Solution:  [Detailed Explanation: Principal is always taken as 100%

Since rate of interest is 5% per annum, so interest for one year (4 - 3) will be 5% × 1 = 5%

In another way, it can also be understand as : At the rate of 5% per annum, the SI for 3 years is 15% and SI for 4 years is 20%, so the difference is (20 -15)% = 5%. Therefore,