Write an expression for double a number 𝑑.
First, let’s think about the word “double.” What does “double” mean mathematically? If you have a double an amount, you have two times that amount. Our number is 𝑑. If we have double a number 𝑑, we have two times the number 𝑑. Two times can be written like this: two 𝑥. Bring down the 𝑑. So we have two times 𝑑.
And there’s one other way we can simplify this expression. When we’re multiplying a variable by a number, we don’t need the multiplication
symbol. We write the two next to the 𝑑. And that means two times 𝑑. This expression represents double the number 𝑑, two times 𝑑.