Question 1157916: 1. A certain bank offers an interest rate of 12; 5% on a one-year fixed deposit and the interest is compounded at the end of the year. Suppose you invest p rands for one year, and at the end of the year the investment is worth R9 000 Calculate p
2. Find the time (in years) that it will take an initial investment of R2250 to double in value at an interest rate of 8,75% per annum, if the interest is compounded quarterly.
(c) In the year 2000 the population of the world was 6,1 billion. The doubling time of the world population is 20 years. In which year will the world population reach 100 billion if it continues to grow at the same rate?
Found 2 solutions by mananth, MathTherapy:
Answer by mananth(16946)   (Show Source):
You can put this solution on YOUR website!
1. A certain bank offers an interest rate of 12; 5% on a one-year fixed deposit and the interest is compounded at the end of the year. Suppose you invest p rands for one year, and at the end of the year the investment is worth R9 000 Calculate p
The Compound interest formula is
A=p*(1+r)^tn
9000=p*(1+0.125)^1
P= 9000/1.125
P=8000 rand
2. Find the time (in years) that it will take an initial investment of R2250 to double in value at an interest rate of 8,75% per annum, if the interest is compounded quarterly.
A=p*(1+r)^tn
4500 = 2250*(1.0875)^4*n
2= 1.0875^4n
log 2 = 4n *log 1.0875
0.3010/4 = n*log 1.0875 ( log 1.0875=0.036)
0.075/0.036 =n
n= 2 years
(c) In the year 2000 the population of the world was 6,1 billion. The doubling time of the world population is 20 years. In which year will the world population reach 100 billion if it continues to grow at the same rate?
A=p*(1+r)^tn
t(2000) = 6.1 billion
n=20
t(2020) = 12.2
12.2=6.1(1+r)^20
2= (1+r)^20
You continue
3.5%
Answer by MathTherapy(10552)  (Show Source):
You can put this solution on YOUR website! 1. A certain bank offers an interest rate of 12; 5% on a one-year fixed deposit and the interest is compounded at the end of the year. Suppose you invest p rands for one year, and at the end of the year the investment is worth R9 000 Calculate p
2. Find the time (in years) that it will take an initial investment of R2250 to double in value at an interest rate of 8,75% per annum, if the interest is compounded quarterly.
(c) In the year 2000 the population of the world was 6,1 billion. The doubling time of the world population is 20 years. In which year will the world population reach 100 billion if it continues to grow at the same rate?
That person's WRONG, as usual! It DOESN'T take 2 years for an amount to double, at 8.75%, compounded quarterly!
As a matter of fact, it takes 
Even when the time's estimated using the Rule of 72, it's 8.23 years.
I wish these people would learn math before they try to help someone!
Giving someone WRONG ANSWERS - as some of them on here do - doesn't bode well for the reputation of those who know what they're doing, and how to really help people who need help!
Can't these people use COMMON SENSE, if they have any, to determine if an answer makes sense? I guess they have NONE!
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