So, you've got a swarm of kobolds and/or rats, and are aggrieved at having to roll large quantities of pairs of dice when they all have advantage? Fortunately, there's an easier way to deal with it.
Say you've got 10 advantagey kobolds rolling against a single target. Roll 10 d20s. Set aside the ones that hit, reroll the ones that miss. This will give you the proper hit/no-hit distribution, but some people will want an accurate crit chance as well. In that case, of the set-aside "hit" dice, reroll the ones that didn't crit - if they come up 20, they crit, otherwise they count as normal hits.
Straightforward procedure, gives accurate results, and there's no need to pair dice up.
Say you've got 10 advantagey kobolds rolling against a single target. Roll 10 d20s. Set aside the ones that hit, reroll the ones that miss. This will give you the proper hit/no-hit distribution, but some people will want an accurate crit chance as well. In that case, of the set-aside "hit" dice, reroll the ones that didn't crit - if they come up 20, they crit, otherwise they count as normal hits.
Straightforward procedure, gives accurate results, and there's no need to pair dice up.