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9 A loan grows to 
$3740 after 1 year and 
$4114 after 2 years with compound interest which is computed annually. Find
(a) the interest rate per annum,
(b) the original loan. 
340^(@)

A loan grows to $3740 \$ 3740 after 11 year and $4114 \$ 4114 after 22 years with compound interest which is computed annually. Find\newline(a) the interest rate per annum,\newline(b) the original loan.

Full solution

Q. A loan grows to $3740 \$ 3740 after 11 year and $4114 \$ 4114 after 22 years with compound interest which is computed annually. Find\newline(a) the interest rate per annum,\newline(b) the original loan.
  1. Establish Relationship Using Compound Interest Formula: First, let's establish the relationship between the amounts after each year and the interest rate. We can use the compound interest formula, which is A=P(1+r)nA = P(1 + r)^n, where AA is the amount of money accumulated after nn years, including interest, PP is the principal amount (the initial amount of money), rr is the annual interest rate (decimal), and nn is the number of years the money is invested or borrowed for.
  2. Set Up Equations for Each Year: We know the loan amount after 11 year A1A_1 is $3740\$3740, and after 22 years A2A_2 is $4114\$4114. We can set up two equations using the compound interest formula for each year:\newlineFor the end of the first year:\newlineA1=P(1+r)1A_1 = P(1 + r)^1\newlineFor the end of the second year:\newlineA2=P(1+r)2A_2 = P(1 + r)^2
  3. Express PP in Terms of A1A_1 and rr: We can use the first equation to express PP in terms of A1A_1 and rr:P=A1(1+r)P = \frac{A_1}{(1 + r)}
  4. Substitute PP into Second Equation: Now we can substitute this expression for PP into the second equation to find rr:A2=(A11+r)(1+r)2A_2 = \left(\frac{A_1}{1 + r}\right) \cdot (1 + r)^2
  5. Simplify Equation and Solve for rr: Simplify the equation by canceling out (1+r)(1 + r) in the numerator and denominator:\newlineA2=A1×(1+r)A_2 = A_1 \times (1 + r)
  6. Calculate r Value: Now we can solve for rr by dividing both sides by A1A_1 and then subtracting 11:
    (1+r)=A2A1(1 + r) = \frac{A_2}{A_1}
    r=(A2A1)1r = \left(\frac{A_2}{A_1}\right) - 1
  7. Express rr as Percentage: Plug in the values for A1A_1 and A2A_2 to calculate rr:
    r=411437401r = \frac{4114}{3740} - 1
    r1.100267379679141r \approx 1.10026737967914 - 1
    r0.10026737967914r \approx 0.10026737967914
  8. Find Original Loan Amount: To express rr as a percentage, we multiply by 100100:r=0.10026737967914×100r = 0.10026737967914 \times 100r10.03%r \approx 10.03\%
  9. Calculate PP Using Values for A1A_1 and rr: Now that we have the annual interest rate, we can find the original loan amount (PP) using the first year's equation:\newlineP=A1(1+r)P = \frac{A_1}{(1 + r)}
  10. Calculate PP Using Values for A1A_1 and rr: Now that we have the annual interest rate, we can find the original loan amount (PP) using the first year's equation:\newlineP=A1(1+r)P = \frac{A_1}{(1 + r)}Substitute the values for A1A_1 and rr (as a decimal) to calculate PP:\newlineP=3740(1+0.10026737967914)P = \frac{3740}{(1 + 0.10026737967914)}\newlineP37401.10026737967914P \approx \frac{3740}{1.10026737967914}\newlineP3399.97P \approx 3399.97

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