Lesson 11 of 16
Words that pick numbers
Show on a big screenA mela stall has 30 tickets, numbered 1 to 30. You pick one ticket without looking. You win with a prime number. What is the chance?
Step 1 of 4
- Thirty tickets, numbered 1 to 30.
- A prime has exactly two factors, 1 and itself. 1 has only one factor.
- The primes are 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29.
- That is 10 of 30. P = 10/30 = 1/3.
10 of the 30 tickets are prime. So the chance is 10/30, which is 1/3.
The rule
Many questions name the numbers in words.
Read each number word. Then list the numbers.
- Factor — a number that divides another with nothing left over. The factors of 6 are 1, 2, 3 and 6.
- Prime number — a number with exactly two factors, 1 and itself.
- Perfect square — a whole number times itself, such as 3 × 3 = 9.
Divisible by 6 means 6 divides the number with nothing left over. A digit is one of 0 to 9. So 12 has two digits.
| Word | It picks | On tickets 1 to 30 |
|---|---|---|
| prime | exactly two factors | 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 |
| perfect square | a whole number times itself | 1, 4, 9, 16, 25 |
| divisible by 6 | 6 goes in with nothing left | 6, 12, 18, 24, 30 |
| two-digit | 10 to 99 | 10 to 30 |
| between 20 and 26 | more than 20 and less than 26 | 21, 22, 23, 24, 25 |
Example. A two-digit number divisible by 6? List the numbers: 12, 18, 24, 30. That is 4 tickets. P = 4/30 = 2/15. The number 6 is left out. It has one digit.
Now try it. Read the words. Tap every ticket that fits.
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Try the lab to finish this lesson.