Rows and columns

Challenge 8 of 16

A times can multiply boxes rather than numbers: total is groups times perGroup, so it is never set by hand. This is how you count a grid without counting it — rows times columns.

Set groups and perGroup to match the target.

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Set groups and perGroup to match the target.

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Lesson Multiplying and Dividing

Multiplying uses a star and dividing uses a slash: var x = 5 * 4; makes 20, and var x = 20 / 4; makes 5. The line is the same shape as adding and taking away — only the sign in the middle changes.

A times is really a shortcut for adding the same number over and over. 4 * 3 is 4 + 4 + 4. Once you see that, multiplying stops being a new idea and becomes a quicker way of writing an old one.

Order does not matter for a times, the way it did not for adding: 3 * 5 and 5 * 3 both make 15. It does matter for a share, like taking away — 20 / 4 is 5, but 4 / 20 is not.

Sharing has one wrinkle. It does not always come out even. 24 / 4 is 6, but 24 / 5 is 4.8 — a number with a decimal point. Nothing is broken when that happens, but in this course the numbers are meant to be whole, so it usually means the two numbers are not a tidy pair.

The second half of this topic does something new: a box can size a shape, not just print a number. circle(200, 200, size); makes the circle as wide as whatever is in size, and if that size is worked out — var size = count * 30; — then changing one small number resizes the whole picture. That is the real reason for all of this.

A last note: a size on screen cannot be judged to the pixel, so where a challenge needs an exact one it tells you the number to aim for.