profit made on the apples sold

Question

I pay $8 for 5 apples. I then sell them at 3 for $10. I bought p apples last week and sold all of them making a profit of $78. find p

Answer 1

8 for 5 bought = cost = c= 8/5= $1.60 per apple

10 for 3 sold = revenue = r= 10/3 =$3.33 per apple

profit =r-c= 3.33-1.6= $1.73 per apple = 10/3-8/5= (50-24)/15= 26/15

total profit = 78=p(r-c)= 26p/15

p= 15(78)/26= 78/1.73= 15(39)/13= 45 apples

45 cost 45x8/5= $72

45 sold for 45x10/3= $150

profit=150-72=$78