Log Utiliy Function Trick I am watching Lecture 3 of Yale's Financial Theory Lecture (by John). At about minute 50 he explains something along this line (with reference to log utility functions). 

MUx/Px=MUy/Py

And simplifies down to: 0.75/Px(x)= 0.25/Py(y)

Given that Px(x)+Py(y)=Total Money

He concludes that "The total spent on x relative to 3/4 is equal to the total spent on y relative to 1/4" and therefore a consumer would spend 3/4 of their income on x and 1/4 on y. 

How is he drawing that conclusion from the above equations?
Start here
$$0.75/p_xx= 0.25/p_yy$$

Multiply both sides by $p_xx p_yy$, you get:
$$0.75p_yy=0.25p_xx$$

Add $0.75p_xx$ to both sides, you get:

$$0.75(p_xx+p_yy)=p_xx$$

So:
$$\frac{p_xx}{p_xx+p_yy}=0.75=\frac{3}{4}$$

And you spend the rest of your budget, so $1/4$ of it, on $y$.