Equity: Price at which margin call is received

CFA Level I Equities
#1

Hello everyone,
In the EOCs of Market organization and structure, the 23 question, asks to compute the price at which the trader will receive a margin call.
The data is the following: stock price = 25, the initial margin = 50%, and the maintanence margin = 30%

I used this formula: Price at which I recieve the MC = P0*(1-initial margin) / (1-maintanence margin)

But it doesnt work out, and the book uses this equation:

Equity per share / Price per share: 12.5 + P -25 / P = 30%

The 2 formulas should get the same result but they do not do, does anyone know why?
Thanks in advance!

#3

Both are correct.

$ 25 × (1-0.5)/(1-0.3) = 17.86

#4

haha yesss, the problem was that when I saw the maintanence margin of 0.30, i automatically thought that 1 - 0.30 was .60 and not .70, so I computed it with .60…

dumbest error