How to Play What Are the Odds—and Check the Probability

What Are the Odds, also called Odds Are, is a dare game played one pair at a time: one person proposes a challenge, the other sets a number range, and both say a number simultaneously. Matching numbers trigger the dare. That is the basic version described by wikiHow.

The useful probability lesson is that “1 in 10” describes a matching chance only under particular assumptions—not a guarantee about what people will choose.

The basic rules

1. Agree on a harmless dare. For example: “What are the odds you’ll speak in rhyme for the next minute?” Anyone should be free to decline or stop without punishment. Avoid dangerous, illegal, costly or humiliating challenges.
2. The challenged player sets the range. Saying “1 in 10” means each player can choose any whole number from 1 through 10, inclusive. It does not mean choosing only 1 or 10.
3. Choose privately, then count down. Say “3, 2, 1,” followed by your chosen numbers at the same time. Neither player should wait to hear the other’s answer.
4. Compare the numbers. If both say 7, the challenged player does the agreed dare, provided they still consent. If one says 7 and the other says 4, no dare is triggered under this basic version.
5. Take turns proposing challenges. No money, equipment or formal scoring is needed.

The range-and-match mechanism is also described in the List of Games rules.

Agree on house rules first

Extra rules are not universal. For instance, List of Games describes a “1 in 2” reversal: matching numbers trigger the challenged player’s dare, while different numbers send it back to the challenger. wikiHow describes an optional replay when the two numbers add up to the range limit, using half the range for the replay—for example, 13 and 7 in a 1-through-20 round lead to a 1-through-10 replay.

For a first game, use matching numbers only. Adding reversals or replays changes the possible outcomes and the probability calculation.

What does “1 in 10” actually mean?

Assume both players choose independently and uniformly: each number from 1 through 10 has an equal chance, and neither choice influences the other.

There are:

• 10 × 10 = 100 equally likely ordered pairs;
• 10 matching pairs, from (1, 1) through (10, 10);
• therefore, a 10 ÷ 100 = 10% chance of a match.

In general, with a range of 1 through N:

Probability of a match = 1 ÷ N, under those assumptions.

A larger range lowers the matching probability under those assumptions. But spoken choices need not be uniform or independent. If both players always choose 7, they match every time, despite calling the range “1 in 10.” Using separate, independent uniform random-number draws would make the calculation fit the game.

Also, a 1-in-10 probability means nine non-matches for every match in the theoretical distribution: 9-to-1 odds against, not 10-to-1. See our guide to probability versus odds.

Why this matters for prediction markets

Consider a hypothetical $1 binary contract on that same round, now using independent uniform random draws. Its rules must specify what counts as a match, which round counts, and which record establishes the result. Actual prediction markets likewise have predefined resolution sources and rules; Polymarket explains these in its resolution documentation.

Suppose the Yes bid is 8¢, the ask is 12¢, and the assumed entry fee is 1¢ per contract. These are illustrative figures, not a live quote or platform fee schedule. Assume one contract is available to buy at that ask.

• Midpoint: (8¢ + 12¢) ÷ 2 = 10¢.
• Spread: 12¢ − 8¢ = 4¢.
• Cost to buy at the ask, including the assumed fee: 13¢.

The midpoint is a reference price, not necessarily your purchase price: Polymarket’s order-book documentation distinguishes the midpoint from the buy-side ask and sell-side bid.

Assuming a $1 Yes payout, $0 otherwise, and no further costs, the expected payout is 10% × $1 = 10¢. Expected net result is therefore 10¢ − 13¢ = −3¢ per contract. The break-even probability is 13%, not 10%.

That is the distinction to carry forward: first define the outcome and estimate its probability; then check the executable price and fees. Use the pre-trade checklist before risking money.