How to Quickly Roll Large Numbers of Dice (DnD Other)
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It can be very unwieldy to roll massive numbers of dice at once. It can take a while for players and DMs alike to do the math and finish accounting for the results, which can slow down the game and grind action down to a halt. This is not a good thing. Therefore, I propose the following guidelines as a solution to this problem, allowing you to quickly "roll" large amounts of dice while still keeping the essential factors of randomness and preserving the range of results.
Rolling Tens of Dice
To roll tens of dice, take the "tens" digit of the number of dice you are rolling, and roll that number of dice. Then, multiply the result by 10. For example, if you wanted to quickly roll 48 six-sided dice, you'd roll 4d6 (the "tens" digit of your number of dice) and multiply the result by 10. So, in the previous example, if you rolled 14, you'd end up with a result of 140. You're not done yet, however, next, roll a d10 and add the result to your roll, then roll a d10 and subtract the result to your roll. In effect, you're adding (1d10-1d10) to your result, giving you a random range of -9 to +9. Note that the average of 1d10-1d10 is zero, which means you're making your result sufficiently random without statistically affecting the average result of your roll. If after you roll 1d10-1d10 you get an "impossible" result (e.g. less than 40 or more than 240 for 4d6), then treat your number as the closest legal possibility, ignoring further addition or subtraction.
After you've resolved the "tens" of dice, you'd roll the remainder normally. I.E. after resolving 4d6x10 for 48d6 in the previous example, you'd roll 8d6 with no modifications.
Rolling Hundreds of Dice
To roll hundreds of dice, take the "hundreds" digit of the number of dice you are rolling, and roll that number of dice. Then, multiply the result by 100. So if you wanted to quickly roll 365 eight-sided dice, you'd roll 3d8 and multiply the result by 100. Basically, the process is similar to the process you go through to roll tens of dice, except you're adding 1d100-1d100 to the result, not 1d10-1d10. Again, use common sense and adjust illogical results.
After you've resolved the "hundreds" of dice, you'd go through the "tens" process described above, THEN you'd roll the remainder normally. Thus, to roll 365d8, you'd roll 3d8x100, 6d8x10, and then 5d8.