Answer:
The answer would be 80 black marbles.
Explanation:
The student chose 10 marbles. 8 of those were black. There are 100 marbles total. Going at this rate, picking 10 at a time, 10x10 is 100. So we would do this 10 times. 8x10 is 80. 2x10 is 20. There are 80 black marbles.