Question

complete the table below
principal (p) rate(r) time (t) interest
2.5% 4 1,500
36,000 1.5 4,860
250,000 0.5% 243
500,000 12.5% 10
formula:
triangle with i, prt
p = \frac{i}{rt}
r = \frac{i}{pt}
t = \frac{i}{pr}

Explanation:

Step1: Find principal in first row

Using the simple - interest formula $I = Prt$, we can solve for $P$ when $I = 1500$, $r=0.025$ and $t = 4$. Rearranging the formula gives $P=\frac{I}{rt}$.
$P=\frac{1500}{0.025\times4}=\frac{1500}{0.1}=15000$

Step2: Find rate in second row

Using $I = Prt$, we solve for $r$ when $P = 36000$, $t = 1.5$ and $I = 4860$. Rearranging gives $r=\frac{I}{Pt}$.
$r=\frac{4860}{36000\times1.5}=\frac{4860}{54000}=0.09 = 9\%$

Step3: Find time in third row

Using $I = Prt$, we solve for $t$ when $P = 250000$, $r = 0.005$ and $I = 293$. Rearranging gives $t=\frac{I}{Pr}$.
$t=\frac{293}{250000\times0.005}=\frac{293}{1250}=0.2344$ (years). To convert to months (assuming we want a more practical time - unit), $t = 0.2344\times12\approx2.81$ months.

Step4: Find interest in fourth row

Using $I = Prt$, when $P = 500000$, $r = 0.125$ and $t = 10$.
$I=500000\times0.125\times10 = 625000$

Answer:

Principal (P)	Rate (r)	Time (t)	Interest (I)
36000	9%	1.5	4860
250000	0.5%	0.2344 (or about 2.81 months)	293
500000	12.5%	10	625000