Question

there are 4 trombones out of 25 instruments in the lander town band. what percent of the instruments are trombones. //percent and fractions

Answer 1

The definition of a percent, according to google.com, is "one part in every hundred".
So 4 trombones out of 25 instruments would represent the same rate as:
16 trombones out of 100 instruments (multiplying both by 4)
Which means, that 16 parts in every hundred instruments in the lander town band would be trombones. Hence, 16% is the answer.

Answer 2

All you have to do is convert the fraction 4/25 into a decimal. 0.16 is the decimal conversion so the band is made up of 16% trombones.