What is the best order-of-magnitude estimate for 0.3?
a. 10^-3
b. 10^-4
c. 10^-5
d. 10^-6

c. 10^-5

For example.
The scientific notation of 70, 030, 000. To find the scientific notation of this value 
1.  We first move the period which separates the whole number from the decimal number which is located after the numbers of the given value. 
2.  We move it in the very recent order number which is seventy million, seven and zero. 
3.  It becomes 7.003
4.  Thus we count how many moves we did from the tens to the ten million order place. 
5.  7.003 x 10^7