One outcome only
An event with a single outcome is an elementary event.
Kritika draws a ball
A bag holds one red, one blue and one yellow ball. Kritika takes out one ball without looking.
Look at two events: "the ball is yellow" and "the ball is red or blue".
Which of these events has only one outcome?
What this lesson covers
The idea
An event having only one outcome is called an elementary event.
Kritika draws a ball
A bag holds one red, one blue and one yellow ball. Kritika takes out one ball without looking.
Look at two events: "the ball is yellow" and "the ball is red or blue".
Which of these events has only one outcome?
- "the ball is yellow"
- "the ball is red or blue"
- both of them
Build events, find the elementary ones
Tap outcomes to build an event. Whenever your event has exactly one outcome, it goes into your list of elementary events. Find all the elementary events of the bag and of the die. Tap again to take an outcome out.
Elementary means one outcome
An event having only one outcome is called an elementary event.
"The ball is yellow" is the event {Yellow}: one outcome, so it is elementary. "The ball is red or blue" is {Red, Blue}: two outcomes, so it is not elementary. It is made of two elementary events, {Red} and {Blue}.
A die has 6 elementary events: {1}, {2}, {3}, {4}, {5}, {6}. The event "a number greater than 4" is {5, 6}, with 2 outcomes, and "a number less than or equal to 4" is {1, 2, 3, 4}, with 4 outcomes. Neither is elementary.
Notes
An event having only one outcome is called an elementary event. A bigger event is made of elementary events.
Check yourself
A die is thrown once. Which of these events is an elementary event?
How many elementary events does a die have?
Answer: 6
{1}, {2}, {3}, {4}, {5}, {6}: 6 elementary events.
Harpreet tosses two coins, one of Rs 1 and one of Rs 2. The outcomes are (H, H), (H, T), (T, H), (T, T). Which event is elementary?
A box has 3 blue, 2 white and 4 red marbles, and each of the 9 marbles is an outcome. How many outcomes does the event "the marble is red" have?
Answer: 4
The event has 4 outcomes, so "the marble is red" is not an elementary event.
- a number greater than 4. This is {5, 6}, which has 2 outcomes. An elementary event has only one.
- an even number. This is {2, 4, 6}, which has 3 outcomes. An elementary event has only one.
- getting a 3 — correct. Yes! {3} has exactly one outcome.
- a number less than or equal to 4. This is {1, 2, 3, 4}, which has 4 outcomes. An elementary event has only one.
- getting (H, T): head on the Rs 1 coin and tail on the Rs 2 coin — correct. Yes! (H, T) is a single outcome.
- at least one head. This has 3 outcomes: (H, H), (H, T), (T, H). It is not elementary.
- at least one tail. This has 3 outcomes: (H, T), (T, H), (T, T). It is not elementary.