Step-by-step explanation:
Let the required number be x.
[tex]\therefore \:x - 40 \% \: of \: x = 30 \\ \\ \therefore \: x - \frac{40}{100} x = 30 \\ \\ \therefore \: x - 0.4 x = 30 \\ \\ \therefore \: 0.6 x = 30 \\ \\ \therefore \: x = \frac{30}{0.6} \\ \\ \therefore \: x = \frac{300}{6} \\ \\ \: \: \: \: \huge \purple{ \boxed{ \therefore \: x = 50 }}\\ \\ [/tex]
Thus, the required number is 50.
