How do you write the standard form of 5 plus 300 plus 8?

Answer 1

Add them up:

5 + 300 + 8 = 513

I suspect that you may have a zero missing:

either: 50 + 300 + 8 = 358

or: 5 + 300 + 80 = 385

Expanded form is usually written with the biggest number first and the rest in decreasing value, ie

358 = 300 + 50 + 8

385 = 300 + 80 + 5

Answer 2

That depends what you mean by "standard form". That is the standard form for an addition. On the other hand, you can actually carry out the addition, and write the result as a single number.

Answer 3

The total, in standard form, is 3.13*10^2