A bowl contains 5 red balls and 5 white balls. Dorothy selects balls at random without looking at them. How many balls must she select to be sure she has at least two red balls?

7

Step-by-step explanation:

To find the answer, consult the worst case. The worst thing that can happen is Dorothy selects the 5 white balls first. Now, only red balls remain. Since Dorothy can only select red balls, the first 2 balls she will pick will be red. 5+2=7. Dorothy must select 7 balls to be sure she has at least 2 red balls.

its a straight line parallel to the time axis