Sandra bought 30 T-shirts at the clothing store. 20% of the T-shirts were blue and half of the T-shirts were black. How many of the T-shirts were neither black nor blue?

So you have 20% of blue and 50% of black.

So you have 70% in total that are both blue and black.

100% - 70% = 30%

So that means 30% were neither blue or black.

Do a proportion

30/100 = x/30

30 x 30 = 900

900 divided by 100 = 9

Answer is 9 shirts are neither blue or black