How do i convert decimal numbers to binary?
I mean numbers like 1.5 or 1.25
Keep multiplying the decimal part by 2:
$\displaystyle 1.5_{10}=1_2+(.5)_{10}$
Now,
$\displaystyle \begin{aligned}.5\times 2 & = {\color{red}1}\text{ R } {\color{blue}0}\\ {\color{blue}0}\times 2 &= {\color{red}0} \text{ R } {\color{blue}0}\\ \vdots\end{aligned}$
So it follows that $\displaystyle .5_{10}=.1_2$. Thus, $\displaystyle 1.5_{10}=1.1_2$
Do something similar for $\displaystyle 1.25_{10}$
Can you take it from here?