An electron has a mass of 9.109 x 10-31 kg. What is the mass (in kilograms) of 2.500 billion electrons?

Just multiply them together.

YOu can use the calc on the home page.

Can I solve it? In order to solve it, I need to know what to multiply.

2.5 x 1 billion x 9.109 x 10^-31    kg

you just have to change 1 billion to a number berfore you start.  You can use google to help you do that Dragon.  :)

So the answer is 2.5 x 1 billion x 9.10900 x ((10^(-31)) kg) = 2.27725 × 10-21 kilograms

I don't know, use the 'calculation' button and she me what you entered please.

I used Google. Just type in the question.

Why don't you do it here with the calculation button and show me that you can?  

I'd like you to do that.