You have 100 BTC in your wallet. For every 10 seconds you can count 10 BTC.
How many seconds will it take to count 80 BTC?
OP, no offence but this is probably the dumbest puzzle, I have ever seen. First of all, how exactly will you count BTC? This is not fiat which you can count.
20?
YES !
And even if we replace BTC with USD in the puzzle, you can't count 80 in 20 seconds as per the question. You can count only 20 in 20 seconds, so you can separate 80 from the remaining 100 but that doesn't mean you can count 80 in 20 seconds. You count 80 in 80 seconds only.