Proportions
A pound of almonds is said to cost 8 dollars.
But one pound is equivalent to 16 ounces, therefore:
16 ounces cost 8 dollars
Dividing by 8 we get that
2 ounces of almonds cost 1 dollar
Thus, for $3.80 we can buy 2*3.80 = 7.60 ounces of almonds
