Question 1068812
It depends on how many payments of {{{R250}}} are required.
The number of payments required should be stated as part of the question.
 
If you have to make only {{{24}}} such payments,
the amount paid in those {{{24}}} such payments adds up to
{{{24*(R250)=R6000}}} ,
and since that plus the {{{R500}}} deposit equals the full price,
{{{R6000+R500=R6500}}} ,
the interest rate would be {{{"0%"}}} .
 
If you have to make {{{30}}} such payments,
the amount paid in those {{{30}}} such payments adds up to
{{{30*(R250)=R7500}}} .
After the {{{R500}}} deposit, there was a debt of
{{{R6500-R500=R6000}}} .
If {{{R6000 was paid in those 30 monthly payments,
the total interest charged was
{{{R7500-R6000=R1500}}} .
That amounts to {{{R1500/R6000=0.25=25/100="25%"}}} of the amount financed.
With that paid over {{{30 months=30/12}}}{{{years=2.5years}}} ,
The simple interest would be {{{"25%"/2.5="10%"}}} .
months
and since that plus the {{{R500}}} deposit equals the full price,
{{{R6000+R500=R6500}}} ,
the interest rate would be {{{"0%"}}} .
 
If you want to write a formula, you could write
{{{I=Prt}}}, where
{{{I}}}= interest paid,
{{{P}}}= amount financed,
{{{t}}}= time in years, and
{{{r}}}= interest rate as a decimal, for example {{{0.12}}} for {{{"12%"=12/100=0.12}}} .
Then, for {{{I=R1500}}} ,
with {{{t=30/12=2.5}}} for {{{30}}} monthly payments,
you would write
{{{R1500=(R6000)r(2.5)}}} , and solve to get {{{r}}} .
{{{R1500)/((R6000)r(2.5))=r}}}
{{{r=0.10}}} (for {{{"10%"}}} interest rate.