chetan2u
magniv123
A merchant invested $10,000 at 5% annual interest, compounded semi-annually,
and an amount of $X at 5% simple annual interest. At the end of the first year, the
total interest earned on each investment was the same. What is the value of X?
a. $10,000
b. $10,125
c. $10,250
d. $10,500
e. $10,825
im looking for a fast way to solve this.
thank you:)
Hi,
I can think of 2 ways..
1) substitution..
Start from the middle value so that you can eliminate 2 choices either one on top or below..
Equation is \(10000(1+\frac{2.5}{100})^2-10000=\frac{10250*5}{100}\)
10000*1.025*1.025-10000~500..
But 10250*.05~ 612..
So it has to be less than 10250.. AND ofcourse it has to be more than 10000
Only value left is 10125..
2) method..
Leave 10000 and take it as 1..
So \((1+\frac{2.5}{100})^2-1=\frac{x*5}{100}\)
1.025*1.025-1=x/20.......0.00506=x/20.....X=0.506*20=1.012..
Ans= 1.012*10000=10120
B
I came up with another fast way..
Because the amount in the first case has been invested semi-annually, we can divide it into two periods of 6 months each.
In the first 6 months the interest earned will be = 250
In the next 6 months the interest will be = 250 + interest on 250
which is 250 + 25/4
Now this total interest earned is equal to 5% of X..
\(250 + 250 + \frac{25}{4} = \frac{5}{100}*X\)
\(X = 10125\)
(B)
This method probably minimizes the calculations.