Two fifths of the instruments in the marching band are brass. One-eighth of the brass instruments are tubas. What fraction of the band is tubas?"

2/5 are brass, 1/8 of 2/5 are tubas

When you have the word "of" you're going to use multiplication.

40% is brass (you know this by dividing 2 by 5 for the 2/5ths ratio), so you'll want to know what 1/8 of that is.

40 * (1/8) = 5 (this is already a percent)

You can also take 1/8 and multiply it by 2/5. You end up with the same thing, but it would be written as. 05. To make this into a percent you multiply it by 100 to get 5%

Your final answer is 5% of the band are tubas.