A deck of six cards
Probability measures likelihood
How likely?
Will it rain today? Will our school win the hockey match? Will my name be picked in the lucky draw? Nobody can say for sure. But we can say how likely each one is.
A deck has 6 cards. Some are purple and the rest are green. You draw one card without looking. How sure can you be that it is purple?
What this lesson covers
The idea
Probability is a type of measurement of the likelihood of events, expressing how certain we are that an event will occur; it is the area of mathematics that studies randomness and chance.
How likely?
Will it rain today? Will our school win the hockey match? Will my name be picked in the lucky draw? Nobody can say for sure. But we can say how likely each one is.
A deck has 6 cards. Some are purple and the rest are green. You draw one card without looking. How sure can you be that it is purple?
- It depends on how many cards are purple
- Always sure
- Never sure
Change the deck
Use the − and + to choose how many of the 6 cards are purple. Watch the meter. Visit every situation from impossible to certain.
Chance can be measured
Probability measures how likely an event is. It tells us how certain we are that the event will happen.
Like length or area, probability is a measurement. But it measures chance, not size. More purple cards in the deck means a purple draw is more likely.
Notes
Probability measures how likely an event is. The more favourable the situation, the higher the probability.
Check yourself
A deck of 6 cards has 5 purple cards. How likely is it that you draw a purple card?
How many of the 6 cards must be purple so that purple and green are equally likely?
Answer: 3
3 purple and 3 green cards: purple and green are equally likely. So 3 cards.
Which one is a random event?
What does probability measure?
- Impossible. There are purple cards in the deck, so it can happen.
- Certain. One card is green, so a green draw can still happen.
- More likely than not — correct. Yes. 5 of the 6 cards are purple, so purple is very likely, though not certain.
- Whether it rains tomorrow — correct. Yes. We know the possible results (rain or no rain), but not which one will happen.
- The number of days in a week. This is always 7. There is no chance in it.
- The sum of 3 and 4. The sum is always 7. Nothing is left to chance.
- How long an event lasts. That is time. Probability measures chance.
- How likely an event is — correct. Yes. It measures how certain we are that an event will happen.
- How big an event is. Probability does not measure size.