Question

Jonathan has a collection of 400 marbles. Blue marbles make up 17% percent of his collection.

Answer 1

So percent means parts out of 100 so 17%=17/100
400 marbles
17% of 400=blue
'of' can be translated to multiply 
17%=17/100
17/100 ties 400=6800/100=68
he has 68 blue marbles.