A decimal number is any number with a nonzero digit to the right of the decimal point. But for the SAT, it’s more important to know that decimals are, like fractions, a way of writing parts of wholes. If you have to add, subtract, multiply, divide, or perform any other operation on a decimal for the SAT, we highly recommend that you use a calculator. It will save more time and you will make fewer mistakes.
Converting Decimals to Fractions
Even if you use a calculator, you should know how to convert decimals into fractions and vice versa. Both conversions are easy to do.
To convert a decimal number to a fraction,
  1. Remove the decimal point and make the decimal number the numerator.
  2. Let the denominator be the number 1 followed by as many zeros as there are decimal places in the decimal number.
  3. Reduce this fraction.
To convert .3875 into a fraction, first eliminate the decimal point and place 3875 as the numerator:
Since .3875 has four digits after the decimal point, put four zeros in the denominator following the number 1:
Then, by finding the GCF of 3875 and 10,000, which is 125, reduce the fraction:
To convert from fractions back to decimals is a cinch: divide the numerator by the denominator on your calculator:
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