Working with whole and decimal numbers is fine in many everyday situations, but there are a few cases where you need to use fractions. For instance, many recipes call for amounts in terms of fractions. You can quickly convert a number to a fraction format by hand using basic math rules.

Understand the basic concept that a fraction has a numerator (number on top) and denominator (number on the bottom).

Look at the entire number after the decimal point then count the number of places after the decimal point. The number of places allows you to determine your denominator so that you can write the number as a fraction.

Place the number after the decimal point over 100 if there are two decimal places, over 1,000 if there are three decimal places and so on into infinity. For example, if the number is .157 the fraction should read as 157/1,000, if the number is .98 the fraction is 98/100 and if the number is .45432874 the fraction is 45,432,874/100,000,000. As a rule of thumb the number of places you count after the decimal point should be equal to the number of zeros you add to 1 to determine the denominator.

Reduce your fraction to the lowest common denominator (if necessary). To do so take the largest number that you can divide evenly into both the numerator and denominator and perform the division calculation. For instance, if the number is .75 the initial fraction is 75/100. However, you can divide both 75 and 100 by the number 25 producing three and four. Thus the ending fraction is 3/4.

Add the whole number before the decimal point in front of the fraction if one is present. So for instance, if the number is 10.157, the way to write the ending fraction is 10 157/1,000.
Tips & Warnings
 You can also convert your number into a fraction using a web calculator like the one offered by WebMath or EasyCalculation to change the number to a fraction.
 To express a whole number (no decimals) as a fraction, simply place the number 1 as the denominator. For example, 10 written as a fraction is 10/1.
References
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