Random Number Between 1 and 30
Thirty outcomes, each with a 3.33 percent chance. Thirty feels like plenty of room, which is exactly why repeats in a handful of draws catch people out.
1 to 30 1
30 possible values, each equally likely. Tick nothing and repeats can happen; that is what random means.
3.33 percent each
Every value from 1 to 30 has a 1 in 30 chance, which is 3.33 percent. That is small enough that no single number should feel expected, and it is why people misread what happens next.
Collisions arrive at seven draws
Draw seven numbers from 1 to 30 and the chance that at least two of them are the same is 53.08 percent. Better than even, from seven picks out of thirty slots. Most people guess that seven draws in a thirty-wide range will come back all different, and most of the time they do not. The reason is that seven draws make 21 different pairs, and each pair has its own chance to match.
The same effect shows the other way round: draw thirty numbers and a particular value, say 30 itself, is still missing 36.17 percent of the time. Getting all thirty values to appear at least once takes about 120 draws on average.
If you need thirty different results
Do not press this button thirty times. It draws with replacement, so duplicates are built in. Paste your thirty items into the random picker or the random name picker, which can remove each one as it comes out.
Uses and a limit
Picking a day in a thirty-day month, calling on one student in a class of thirty, choosing a task from a month-long list, assigning thirty lockers. What it is not for is a prize draw with money behind it. The number comes from your browser’s ordinary random function, the page keeps no record and no timestamp, and nothing here could prove afterwards how the draw ran. For a thirty-one day month use 1 to 31.