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MathNet 2015-part-02 — 191 problems (EN–VI) Question 57

Math Olympiad Vault · MathNet 2015-part-02 — 191 problems (EN–VI)

Question 57

In a box, there is one red and five white balls marked by numbers $1$, $2$, $3$, $4$ and $5$. Without looking, Domagoj draws one ball at a time until he draws the red ball and then he stops. Drawn balls are not returned into the box. What is the probability that the sum of the numbers on the drawn balls is at least $10$?