Probability is the chance that something will happen. Will it rain today? Will you pick an apple from the bowl? Probability helps us answer these questions with a number!
Probability is always a number between 0 and 1:
Think of it like this:
Imagine a bag with 6 fruit — 3 apples, 2 bananas, 1 orange. If you reach in without looking, what do you get?
Good news — probability can be written three different ways and they all mean the same thing! Let's use the apple example (3 apples out of 6 fruit):
As a fraction — 3/6 or 1/2
3 favourable ÷ 6 total. Read as "3 out of 6".
As a decimal — 0.5
Just divide the fraction: 1 ÷ 2 = 0.5
As a percentage — 50%
Multiply the decimal by 100: 0.5 × 100 = 50%
Quick conversion table
Probability shows up everywhere! Here are some everyday examples:
The formula
Probability = Number of ways it can happen ÷ Total number of outcomes
Some things will never happen, and some things will always happen. These are the two ends of our probability scale!
Probability = 0 · Impossible
· Rolling a 7 on a normal dice (it only goes to 6!)
· The sun rising in the west
· Picking a grape from a bag of only apples
Probability = 1 · Certain
· Rolling a number less than 7 on a normal dice
· The sun rising tomorrow morning
· Picking a fruit from a bag full of fruit
All probabilities must add up to 1
If probability of rain = 0.3, then probability of no rain = 0.7. Together: 0.3 + 0.7 = 1. This always works!