A grocer bought a box of soap containing 72 bars for $49. Some bars he sold at 3 bars for $2.50 and the rest were sold at 70 cents a bar. This gave a profit of $7.80. How many bars did he sell at each price?

Question

anonymous · Answer

he has 72 bars so a+b=72
also the 3 for 2.5 would make it  aprox. .83 a bar
so it would also be .83a+.70b=56.80
solve for a or b and substitute
.83(72-b)+.70b=56.80
59.76-.83b+.70b=56.80
59.76-.13b=56.80
-.13b=-2.96
b=22.76
23 bars at .70
and 49 bars 3 for 2.50