A bag has 3 candies: strawberry, lemon, and mint. One is picked at random. What is the probability of picking a strawberry candy?
Answer: P(strawberry) = 13 ≈ 0.33.
Step-by-step solution
Idea: S = {strawberry, lemon, mint}: 3 equally likely outcomes, 1 of them favourable.
- S = {strawberry, lemon, mint}, n(S) = 3. Favourable: strawberry, 1 outcome.½ mark
- P(strawberry) = 13 ≈ 0.33.½ mark
P(strawberry candy) = 1/3.
Check: Each flavour has probability 13 and 13 × 3 = 1 ✓.
Answer to write in the exam
S = {strawberry, lemon, mint}; n(S) = 3
Favourable outcomes = 1
∴ P(strawberry) = 13
Common mistakes that cost marks
- Writing 12 (“strawberry or not strawberry”). Those two results are not equally likely; there are three equally likely candies.
- Writing 3 instead of 13. A probability can never be more than 1.
- Writing 13 as 0.3. As a decimal it is 0.333…, about 0.33.
How this can come in the exam
MCQ (1 mark)
A box has 5 pens of different colours: red, blue, black, green and pink. One pen is taken at random. The probability that it is not black is
- 15
- 25
- 35
- 45
Show answer
(D) 45
4 of the 5 pens are not black: 45.
MCQ (1 mark)
A jar has 2 orange, 1 lime and 1 cola sweet. One is picked at random. The probability of an orange sweet is
- 14
- 13
- 12
- 23
Show answer
(C) 12
2 of the 4 sweets are orange: 24 = 12.
Try one yourself
A plate has 4 laddoos: besan, coconut, motichoor and rava. One is picked at random. What is the probability that it is coconut?
Show answer
14.
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