Cogito
Grade 7 Math · Chapter 9 · Lesson 1
Probability as a Number
From impossible to certain, on a scale of 0 to 1.
10 problems · about 17 minutes · 7.SP.C.5, 7.SP.C.7
What this lesson teaches
The child expresses probability as a number from 0 to 1 and computes simple probabilities.
- Probability runs from 0 to 1.
- For equally likely outcomes, divide wanted by total.
- The chance something does not happen is 1 minus the chance it does.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — When Three Measurements Fix a Triangle: Can sides 4, 4 and 9 make a triangle? 1 for yes, 0 for no.
Answer 0
Why No — 8 is less than 9.
Review — Angle Pairs: Supplement of 130°?
Answer 50
Why 50°.
Warm Up
Straightforward practice. Get the method working first.
4 problemsA fair die. Out of 6, how many outcomes are less than 3?
Answer 2
Why 2 out of 6.
What range does a probability lie in?
Answer Between 0 and 1.
Why 0 to 1 inclusive.
A fair die. Out of 6, how many outcomes are odd?
Answer 3
Why 1, 3, 5.
5 red and 5 blue. Out of 10, how many give blue?
Answer 5
Why Half.
Build It Up
The same ideas with more to keep track of.
2 problemsWhat is the probability of something certain?
Answer 1
Why Top of the scale.
What is the probability of something impossible?
Answer 0
Why Bottom of the scale.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Bag: 3 red and 7 blue. Out of 10, how many outcomes give red?
Answer 3
Why 3 out of 10.
The Die: A fair die. Out of 6, how many outcomes are greater than 4?
Answer 2
Why 2 out of 6.