capm calculation fractions / % confusion of companies debt to equity ratio

I do actually make this point in my lectures :-) If equity is 75% and debt is 25% then you use 75 and 25 in the formula (and the total is 100). If on the other hand, debt to equity is 1:4, then for every $1 debt there is $4 equity, so a total of $5. The debt is 20% (1/5) and equity is 80% (4/5) and so you use 80 and 20 in the formula.

You are welcome :-)