80% of a number is equal to the 4 5 th of the other number. what is the ratio between the first number and the second number respectively ?

Answer: Option D

Let the first number be x and second number be y
According to the question,
$$\begin{array}{rl}& 80\%\text{ of }x=\frac{4}{5}\text{of }y\\ & \Rightarrow \frac{80\times x}{100}=\frac{4\times y}{5}\\ & \Rightarrow \frac{4x}{5}=\frac{4y}{5}\\ & \Rightarrow x:y=1:1\end{array}$$