Incorrect. Multiplied the rate of each person by 1/2. Should have instead divided each rate by 1/2. Equivalently, the denominator of each rate--which is the time that it takes each person to wire a classroom--should have been divided by two, as shown in the image below.
Incorrect. There is only one way to pick at least one of each of the four colors, and not 24 ways (4! = 4 x 3 x 2 x 1) as I originally thought. The problem then becomes the number of ways to choose from four colors for each of the two remaining notebooks. Next, there are only four ways to choose two of the same color. What remains is the number of two color combinations. In other words, the number of ways to choose two from four items: 4C2 = 4! / (2! x 2!) = 4x3x2x1 / 2x1x2x1 = 24/4 = 6. Finally, add 4 and 6 to get the final answer of 10 for the second question.