You might try pouring the mess into a colander or sieve and gently shaking it. The flour should run through the mesh while the cornflakes stay behind.
If I use 2 cups of flour from a 20 pound bag of flour how much is left
Most flour comes in a 5 pound bag or a 10 pound bag.
five
depends on how much flour you have. if you have 25 pound bag of flour it would be maybe 14
That is approximately 160 cups of flour.
The way I think that you or most people can use it is to open the bag and pour as much flour as you need to make whatever you are making.
Maybe .25-flour is dirt cheap for a bag.
About 10 cups
You need a 1.5 kilo bag
because
5 pounds
There are 3.6 cups in 1 pound of flour, or 18 cups in a 5 pound bag of flour.