This variation of the Knapsack Problem allows you to take a fraction of an item and place it in the knapsack.
If we have item 1 : 10, item 2 : 20 and item 3 : 30
and Weight W = 20
the fractional knapsack can hold whole Item 1 and partial 20/2 =10 (because there is only remaining 10 available) of Item 2 that’s why it’s called fractional knapsack.