Question over combinations A t-shirt is being sold in 8 colors, 4 sizes, collared or tee, and long sleeve or short sleeve. a. How many different shirts are being sold? b. What if collared shirts only come in 5 colors and 2 sizes? For a, it would simply be $8*4*2*2=128$ combinations right? For b, it would be $5*4*2=40$ combinations right?

You got a) right. In b), you counted only the collared shirts, the second type should also be included.