A store sells a certain product at a fixed price per unit. At the product's current price, w units cost a total of exactly $300. If the price were lowered by $5 from its current value, then w + 2n units would cost exactly $300; if the price were raised by $5, then w – n units would cost exactly $300. What is the value of w? Choose the most appropriate option:
A) 10
B) 15
C) 20
D) 25
E) 30
It got too complicated when I used algebra. Using plugging in, it was quite fast.   Price Quantity total value   p w pw = 300   p-5 w+2n (p-5)(w+2n) = 300   p+5 w-n (p+5)(w-n) = 300   Solving three equations for three unknowns. Tough!!   Plugging in, I always start with C. 20 was the answer here, so saved calculation!   Putting values in above equations:   Price Quantity total value   15 20 300   10 20+2n 300 -&gt; 10(20 + 2n)=300 -&gt; 200 +20n = 300 -&gt; 20n = 100 -&gt; n =5   20 15 300   So w = 20 satisfies all equations!!
<result>C</result>
A store sells a certain product at a fixed price per unit. At the product's current price, w units cost a total of exactly $300. If the price were lowered by $5 from its current value, then w + 2n units would cost exactly $300; if the price were raised by $5, then w – n units would cost exactly $300. What is the value of w?