How do you write \[\dfrac{8}{{20}}\] as a decimal.

Hint: Here in this question, we have to convert the given number into decimal. The given number is in the form of fraction, to convert the fraction number to the decimal we divide the given number by the number which is in the denominator. And then we obtain the required answer.

Complete step-by-step answer:
 The number can be converted from one form to another. Here in this question we have to convert the fraction number into a decimal number. The fraction is a proper fraction where the value of the numerator is less than the value of the denominator. We can’t divide the number 8 by the number 20. By taking the decimal point in quotient we can solve the problem. By decimal point we can carry the zero to the number.
Now consider the number \[\dfrac{8}{{20}}\], on applying division we have

When we take a decimal point in the quotient the number 8 will become 80. Then we can divide the number 80 by 20. When we multiply the number 4 times, we get 80. We get the remainder as zero.
Hence, we have converted the fraction into the decimal number.
Therefore, the decimal form or value for the fraction number \[\dfrac{8}{{20}}\] is 0.4.
So, the correct answer is “0.4”.

Note: The decimal numeral system is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers of the Hindu–Arabic numeral system. The way of denoting numbers in the decimal system is often referred to as decimal notation.