How do you write 4,100 in scientific notation?
Move the decimal three places to the left to make only one digit to the left of the decimal. Scientific notation is written as one number to the left of the decimal.
Keep the one because it is significant it had to have been measured or it would not have been written. The two zeros are not retained because they are just place holders not measured and not significant. Scientific notation only retains the numbers that are significant that is have been experimentally measured
Moving the decimal three places to the left is the same as dividing by 1000. So to keep the value the same it is necessary to multiply by 1000.