Grade 7 › G7U10 Probability

Grade 7 › G7U10 Probability › L1
GRADE 7 · ALBERTAOUTCOME AB-G7-SP4

L1 · Expressing probability: ratio, fraction, percent

Learning goal

“I can express the probability of an event three ways - as a ratio, a fraction and a percent - always using favourable outcomes out of ALL possible outcomes.”

Probability — a number that describes how likely an event is, from 0 (impossible) to 1, or 0% to 100% (certain).
Outcome — one possible result of an experiment, like rolling a 4 or drawing a red marble.
Favourable outcome — an outcome that makes the event happen. If the event is "draw a red marble," every red marble is a favourable outcome.
Event — the result you are interested in, described in words before you count anything.
Worked example

A bag holds 4 red marbles and 6 green marbles. Step 1: Name the event first: "draw a red marble." Favourable outcomes: the 4 red marbles. Step 2: Count ALL possible outcomes: 4 + 6 = 10 marbles in total. Step 3: P(red) = favourable / total = 4/10 = 2/5. As a percent: 2/5 = 40%. Step 4: P(green) = 6/10 = 3/5 = 60%. Check: 40% + 60% = 100% - every draw is red or green, so the two probabilities must complete the whole. Model both ways: the bag drawn as 10 marble circles with the 4 red ones circled, AND the probability placed on a 0%-100% number line - 40% sits between "half as likely as not" territory and impossible, closer to 50% than to 0%. Say it plainly: the bottom number is ALWAYS the total number of possible outcomes - never just "the other group."

Check yourself — explain it

In P(red) = 4/10, what does the 10 stand for?

Paired problem — example still visible

A spinner has 10 equal sections; 3 are yellow. What is P(yellow) as a fraction and a percent? -> 3/10 = 30%

Faded completion — last step is yours

"Rolling a six-sided die: P(rolling an even number) = 3/6 = 1/2 = ___ %." -> 50%

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

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