Write the following fractions as decimal numbers:

(i) $\dfrac{5}{8}$

(ii) $2\dfrac{31}{125}$

(iii) $13\dfrac{7}{40}$

(i) Converting the fraction $\dfrac{5}{8}$ into a decimal,

$\dfrac{5}{8} = \dfrac{5 \times 125}{8 \times 125} = \dfrac{625}{1000} = 0.625$

Therefore, the decimal form is 0.625.

(ii) Converting the fraction $2\dfrac{31}{125}$ into a decimal,

$2\dfrac{31}{125} = 2 + \dfrac{31}{125} = 2 + \dfrac{31 \times 8}{125 \times 8} = 2 + \dfrac{248}{1000} = 2 + 0.248 = 2.248$

Therefore, the decimal form is 2.248.

(iii) Converting the fraction $13\dfrac{7}{40}$ into a decimal,

$13\dfrac{7}{40} = 13 + \dfrac{7}{40} = 13 + \dfrac{7 \times 25}{40 \times 25} = 13 + \dfrac{175}{1000} = 13 + 0.175 = 13.175$

Therefore, the decimal form is 13.175.