The full bag of peanuts weighs 3/4 pound.
But then someone ate 1/3 of the peanuts, and the bag is now only 2/3 full.
This means that there is only two-thirds of the original 3/4 pound remaining now.
This can be simply solved by: 3/4 * 2/3 = 2/4 = 1/2 pound
Hope this helps :)