Independent is what they can change, being the amount he buys. The dependent is the price of each bagel.
We have to choose 3 teachers from a group of 7 teachers, then, the amount of combinations is given by
We have to choose 3 students from a group of 8 students, then, the amount of combinations is given by
Since we have to choose a committee simultaneously formed by 3 teachers and 3 students, we want the intersection of those combinations, which is given by their product
The formula for a combination is given by
Then, we have
Each gray square: 2x2=4 tiles. 6 gray squares: 6x4=24 tiles.
Total number of tiles: 12x10 = 120, 24 of those are gray.
So 120-24 = 96 are white.
96-24 = 72 more white than gray