What is the interest earned, in dollars, if $800 is invested for x months at a simple interest rate of 3% per annum? A - HSC - SSCE Mathematics Standard - Question 9 - 2019 - Paper 1

To find the interest earned using the simple interest formula, we use:

$I = P imes r imes t$

Where:

• I = Interest earned
• P = Principal amount ($800)
• r = Interest rate per period (annual rate divided by the number of periods per year)
• t = Time in years

Given:

• The principal amount, $P = 800$.
• The annual interest rate, $r = 3\% = 0.03$.
• Time in years, since the investment is for x months, we convert months to years: $t = \frac{x}{12}$

Substituting the values into the formula:

$I = 800 \times 0.03 \times \frac{x}{12}$

Simplifying this:

$I = 800 \times 0.03 \times \frac{1}{12} \times x = 800 \times 0.0025 \times x = 2 \times x$

Thus, the answer is 2x.