Hi there!
If Andrea bought 12 bagels and 2/3 were multigrain we can determine what the total amount of bagels that are multigrain by finding a common denominator. We can do this by multiplying 2/3 * 4 which gets us the common denominator we need.
2/3 * 4 <--- Equation
8/12 <--- Simplified from step 1.
Therefore 8 out of the 12 bagels Andrea bought were multigrain!
