In this KS1 Maths article you'll learn what number lines are and how to add and subtract using them. We also have KS1 Maths videos, a quiz and lots of examples.

A perfect number equals the sum of its divisors (excluding itself); 6 is perfect because it’s divisible by 1, 2 and 3 and equals the sum of 1 + 2 + 3. The second perfect number is 28.