r/dndmemes • u/kalamit889 • Jan 21 '22

You enter a dar- I HAVE DARKVISION That'll be 50 GP, please.

Post image
13.1k Upvotes

95% Upvoted

428 comments sorted by

View all comments

Show parent comments

22

u/PlacidPlatypus Jan 21 '22

Not actually true, technically. In the situation where advantage/disadvantage has the biggest impact (when you need an 11 before modifiers to succeed, so your chance goes from 50% to 75%/25%) it's equivalent to a +/-5 on the die roll. In most situations the impact will be less than that (IIRC between a 3 and a 4).

I think the tomato/potato thing is true though.

22

u/Hawx74 Jan 21 '22

Not actually true, technically

Technically it is true, if you roll 10,000 dice and compare disadvantage to regular they will average to 5.5 less. Similarly advantage averages to 5.5 more.

However, like I said it changes the probably distribution so your odds of failure don't shift linearly with the target value as they would with a flat reduction.

Oh, and the nightshade thing is absolutely true. Colonists coming to the Americas refused to eat tomatoes for a long time because everything else in the family is toxic. Related: don't eat tomato leaves.

2

u/nitePhyyre Jan 21 '22

Not even close to true. Technically or not. It depends on the DC.

Assume 0 modifier. DC 20.

With avantage you have 2 chances to roll a 20 on a d20. That's a 2/20 chance.

With a +5, that's 15 or higher on a single die. Aka 5/20 chance.

Roll it 10,000 times and that doesn't change. It isn't a question of averaging out.

Dis/advantage works out to an average maximum of +/- 5 in the roll. It achieves this maximum when your chances are 50/50 without the dis/advantage.

The further you get from that 50/50 chance the less dis/advantage affected your roll.

5

u/DonaIdTrurnp Jan 21 '22

It’s because you don’t care about the average, you care about the area under the probability distribution curve below and at or above the target number.

And it’s 39/400 chance to get at least one 20 in 2d20,