A box holds 60 discs numbered 1 to 60. One disc is drawn at random…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A box holds discs numbered to . One disc is drawn at random. Find the probability that it shows (a) a two-digit number, (b) a perfect square.
Need a reminder? The key ideaShow
For balls, discs or spinners with equally likely outcomes, . To find an unknown number of balls, write the probability with the unknown and solve the equation. An event and its complement add up to .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Two-digit numbers. From to there are numbers: .
Step 2. Perfect squares. : discs, so .
Answer: (a) , (b) .
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