Question 921486
{{{P}}} price of the item, in $
${{{10}}}= what Jerilyn would save on that item using the $10 coupon.
${{{0.15P}}}= what Jerilyn would save on that item using the 15% discount coupon.
THE MATH CLASS ANSWER:
If {{{0.15P=10}}}<--->{{{P=10/0.15}}}<--->{{{P="66.66666 ..."}}} , Jerilyn would save the same amount using either coupon.
For more expensive items, the 15% discount coupon saves more money:
{{{0.15P>10}}}<--->{{{P>10/0.15}}}<--->{{{P>"66.66666 ..."}}} .
For less expensive items, the $10 coupon saves more money:
{{{0.15P<10}}}<--->{{{P<10/0.15}}}<--->{{{P<"66.66666 ..."}}}
 
THE REAL WORLD ANSWER:
Actually, a 15% discount should be rounded to the nearest cent,
so 10.005 would be rounded to 10.01,
and 9.994 would be rounded to 9.99,
but anything in between would be rounded to 10.00.
That means that 15% off {{{P=10.005/0.15=66.70}}} would be rounded to {{{10.01}}} and the 15% discount would be better,
but 15% off {{{P=66.69}}} would be rounded to {{{10.00}}} and both coupons would save the same amount.
A 15% off {{{P=9.995/0.15="66.63333 ..."}}} would be rounded to {{{10.00}}} ,
but 15% off {{{P=66.63}}} would be rounded to {{{9.99}}} , and that would make the $10 off coupon a better bargain.
In conclusion,
Jerilyn should use the $10 coupon for prices up to $66.63,
and the 15% discount coupon for prices from $66.70 up.
For prices in between ($66.64 to $66.69) she could use either coupon.