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Prime Time

What is a factor?

You share 12 idlis. 3 for each of 4 friends. Nothing is left over.

12 dots in one row: 1 × 12.
Step 1 of 5
  1. 12 dots in one row: 1 × 12.
  2. Regroup into 2 rows of 6: 2 × 6.
  3. Regroup into 3 rows of 4: 3 × 4.
  4. Factors of 12: 1, 2, 3, 4, 6, 12.
  5. 7 fits only one row. Factors of 7: 1, 7.

The rule

A factor divides a number exactly, with nothing left over. 4 is a factor of 12: 12 ÷ 4 = 3. 5 is not: 12 ÷ 5 leaves 2 over.

Every number is a factor of itself. 1 is a factor of every number too. Check with 12: 12 ÷ 12 = 1 and 12 ÷ 1 = 12.

Slide the number in the lab. See all its factors.

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This track

  1. 0 Start here
  2. 1 What is a factor?
  3. 2 Counting up in steps
  4. 3 Primes: exactly two factors
  5. 4 Composites: more than two factors
  6. 5 Quick tests without dividing
  7. 6 Numbers that share factors
  8. 7 The big picture
  9. 8 Track quiz

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