In an election between two candidates, the defeated candidate secured 42% of the valid votes polled and lost the election by 7,68,400 votes. If 82,560 votes were declared invalid and 20% people did NOT cast their vote, then the invalid votes were what percentage (rounded off to 1 decimal place) of the votes which people did NOT cast?

6.8 Percent

Percentage of total valid votes that winning candidate secured = (100 - 42) = 58%

% difference b/w the winning and defeated candidate = 58 - 42 = 16%

So, the total number of valid votes = \(\frac{768400}{100}\) × 100 

 = 4802500

Total number of votes (both valid and invalid) = 4802500 + 82560 = 4885060

Total number of voters =  \(\frac{4885060}{(100-20)%}\) = 6106325

Number of people who didn't case vote = 6106325 × 20% = 1221265

Now, % =  \(\frac{82560}{ 1221265}\) × 100% = 6.7602% 

= 6.8%(approx)