Answer: D) 2/5
========================================================
Explanation:
Let's pick a large value such as 1000
So let's say 1000 people were surveyed.
Of those 1000 people, 80% are registered voters. That means we have 0.80*1000 = 800 registered voters. Note how 800/1000 = 0.80 = 80%
Of those 800 registered voters, 75% of them voted in the last election.
This means 0.75*800 = 600 of the registered voters participated in the last election.
So 1000-600 = 400 registered voters did not participate in the last election
This forms the fraction 400/1000 = 4/10 = 2/5 which points us to choice D as our final answer.
It's like saying we had 5 people total, and 2 of them didn't vote in the last election.
Side note: The fraction 2/5 turns into 0.40 = 40%
