Question

How do you write the number 2.17 × 109 in standard form?

Answer 1

Assuming you mean
\[2.17 \times 10^{9}\]
Then here is the method that I would use:
Starting at the decimal point, "hop" to the right 9 times. I don't know a good way to explain it, so I'll just show you:

See how there are nine curves? In each curve that doesn't already have a number, fill in a zero:

Hope this helps :)