the point of intersection on the graph are (3,-2)
0.8p - 50 < = 150
0.8p < = 150 + 50
0.8p < = 200
p < = 200/0.8
p < = 250
the reason I set it up this way is because when it is 20% off, u r actually paying 80% of the original price (p)....80% of the original price is written as 0.8p...then u subtract ur 50 dollar discount coupon...- 50.....and if all she can spend is 150....it would be less then or equal to 150. So the most she can spend on the phone is 250
You will save $522 by paying cash. 165*24=3960 3960-3438=522
:)
