Maths · Rung 10 of 30

Divisibility

A number is prime if only 1 and itself divide it. The greatest common divisor (gcd) is the largest number dividing both; the least common multiple (lcm) is the smallest number both divide. Trick: gcd × lcm = a × b.

Where this sits

This is where the ladder starts: nothing is needed before it.

Exercises from this rung

Generated by the app, from easiest to hardest

  1. gcd(8, 24)

    • 1
    • 8
    • 24
    • 4

    Why The common divisors of 8 and 24: the largest is 8. 8 = 8 × 1 and 24 = 8 × 3, and 1 and 3 share no divisor.

    easier

  2. gcd(6, 14)

    • 2
    • 6
    • 4
    • 42

    Why The common divisors of 6 and 14: the largest is 2. 6 = 2 × 3 and 14 = 2 × 7, and 3 and 7 share no divisor.

    in between

  3. How many divisors does 30 have?

    • 6
    • 9
    • 7
    • 8

    Why The divisors of 30 are 1, 2, 3, 5, 6, 10, 15, 30: 8 in all.

    harder