Store A has a weekend sale. To the nearest hundredth of a percent, what discount must Store A offer for you to buy the system there?

We are given the cost of the product along with the markup percentage.  The markup is how the store makes a profit.  To figure out the markup price, simply multiply the "cost to store" by 100% plus the markup percent.

So the markup prices per store is:

A = 162 * 1.4 = $226.80
B = 155 * 1.3 = $201.50
C = 160 * 1.25 = $200.00

Clearly, the best deal is store C.  So in order to choose store A, we want to pay less than the price of Store C, $200.  So if Store A cost $199.99, then we would purchase there instead of Store C.

Therefore, $226.80 - $199.99 = $26.81
If Store A offered a discount of $26.81, we would purchase from Store A.

$26.81/$226.80 = 0.1182

So we would need a discount of 11.82% from Store A.