This is a matter of elimination. So let's figure out how many of each display there is.
30% of 150 = 0.30 * 150 = 45 displays about electricity.
2/5 * 150 = 0.40 * 150 = 60 displays about renewable energy
1/10 * 150 = 150/10 = 15 displays about gas.
The rest of the displays are about nuclear power. So
150 - 45 - 60 - 15 = 30 displays about nuclear power. Since we want a fraction, we get 30/150
But 30/150 isn't in it's simplest form. The largest number that will evenly divide both 30 and 150 is 30. So divide both the numerator and denominator by 30
(30/30)/(150/30) = 1/5
So 1/5 of the displays are about nuclear power.</span>
