If you are multiplying, you are simply putting the fraction that is listed in, but when dividing, you use the reciprocal of the fraction.
9 x 1 = 9
9 x 2 = 18
9 x 3 = 27
9 x 4 = 36
9 x 5 = 45
9 x 6 = 54
9 x 7 = 64
9 x 8 = 72
9 x 9 = 81
9 x 10 = 90
1. 641
2. 65.4
3. 21+7=28 total marbles. The greatest number of groups would be 7, with 1 blue and 3 white.
4. 80% of 685= .80 x 685= 548 students.