Well, I'll go along with your single digit, but I must respectfully
take issue with your choice of exponent.
10^10 is the number 10,000,000,000 .
Multiply your '4' by that number, and you get 40,000,000,000 .
That's not a very good estimate for 0.00000394.
Let's back up a step.
You're given 0.00000394 .
To turn this into 3.94, you move the decimal point 6 places that way ==> .
That's the same as 10⁶.
But wait ! When you do that, you've changed the value of the number
by 10⁶, and that's a big no-no. So you must immediately do something
that restores it to its original value . . . Multiply it by 10⁻⁶ .
So far, we've decided that 0.00000394 = 3.94 x 10⁻⁶ .
Since they want a single digit, we'll round the 3.94
to the nearest whole number.
4 x 10⁻⁶ .
