The dot array has 6 rows of 14 dots, split by the orange dashed line into 10 blue columns and 4 green columns. Using the split, $6\times 14=6\times 10+6\times 4$. How many dots are there?

Adding two whole numbers always gives a whole number — addition is **closed** on whole numbers. Multiplying two whole numbers always gives a whole number — multiplication is **closed** too. But subtraction is **not** closed: 5 − 7 = −2, which is not a whole number. Division is also not closed: 7 ÷ 2 = 3.5, not a whole number. Closure is the property that lets us trust an operation never to take us 'outside' the world of whole numbers.