How to convert a fraction to a decimal
To turn a fraction into a decimal, divide the numerator by the denominator. If the division ends, the result is a terminating decimal, like 1/8 = 0.125. If the division never ends and some digits repeat, the result is a repeating decimal, like 1/3 = 0.333... The calculator runs the long division with exact numbers and marks the repeating block in parentheses, for example 0.58(3).
When a fraction becomes a repeating decimal
Once simplified, a fraction gives a terminating decimal only when the denominator has no prime factors other than 2 and 5. Any other factor, such as 3, 7, or 11, makes the digits repeat. The length of the repeating block never exceeds the denominator minus 1.
How to convert a decimal to a fraction
A terminating decimal becomes a fraction by putting its digits over a power of 10 with as many zeros as decimal places. Then simplify: 0.375 = 375/1000 = 3/8. For repeating decimals, use the third card, which finds the fraction with the classic method of subtracting the non-repeating part.
Practical example
In a recipe, 3/8 of a cup of milk equals 0.375 of a cup. A 1/6 discount on an item works out to 0.1666..., or about 16.67%.