Write the following percents as decimals

Explanation

We will drop the % symbol and divide each given number by 100 by moving the decimal point two places to the left.  To find the quotient of a decimal and 100, we move the decimal point to the left in the same number of places as there are zeros in 100.

Solution

1. Write 310% as a decimal
   • Write the whole number 310 in decimal notation: 310 = 310.0
     • 310% = 310.0%
   • Drop the % symbol and divide 310 by 100 by moving the decimal point 2 places to the left
     • = 3.100
   • Drop the unnecessary zeros to the right of the 1
     • = 3.1
   • 310%, written as a decimal, 3.1
2. Write 0.9% as a decimal
   • Drop the % symbol and divide 0.9 by 100 by moving the decimal point 2 places to the left.  This requires that a placeholder zero (shown in blue) be inserted in front of the 0.
     • 0.9% = .009
   • Write a zero to the left of the decimal point
     
     • = 0.009
   • 0.9%, written as a decimal, is 0.009