Apply probability to slightly more complex situations, including combined events with dice and cards.
When two dice are rolled together, there are 6 × 6 = 36 total possible outcomes. Counting how many of those outcomes match a condition gives the probability of that event.
Two dice are rolled. What is the probability that both show the same number?
There are 6 matching pairs (1,1),(2,2)...(6,6) out of 36 total, so probability = 6/36 = 1/6
Two dice are rolled. What is the probability that the sum is 7?
There are 6 ways to get a sum of 7: (1,6),(2,5),(3,4),(4,3),(5,2),(6,1), so probability = 6/36 = 1/6
The probability that an event does NOT happen is 1 minus the probability that it does happen, since all outcomes together must add up to 1 (certainty).
The probability of rain tomorrow is 0.3. What is the probability it does NOT rain?
1 − 0.3 = 0.7
A bag has a 2/5 probability of drawing a red ball. What is the probability of NOT drawing red?
1 − 2/5 = 3/5
1. Two dice are rolled. What is the probability that the sum is 8?
2. Two dice are rolled. What is the probability that both show an even number?
3. The probability of drawing a face card from a deck is 3/13. What is the probability of NOT drawing a face card?
4. A weather forecast gives a 0.65 probability of sunshine. What is the probability it is NOT sunny?
5. Two dice are rolled. What is the probability that the sum is 12?
From Rational Numbers to Probability — the entire Class 8 Selina Concise Maths book is done. On to bigger challenges ahead!
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