fskilnik
GMATH practice exercise (Quant Class 19)
If the raining season in Jerusalem begins, Dora estimates a 20% probability of traveling to Israel next holidays. If it doesn´t, she guesses her probability of taking this trip is 250% higher. Based on these assumptions, what are Dora´s chances of traveling to Israel next holidays, if she knows there is a 70% probability for the raining season in Jerusalem to begin?
(A) 15%
(B) 29%
(C) 35%
(D) 42%
(E) 46%
Yes,
ss13ny , your solution is correct! Thanks for joining!
The official solution follows:
\(? = P\left( {{\rm{Dora}}\,\,{\rm{travels}}} \right)\)
\(P\left( {{\text{season}}\,\,{\text{raining}}} \right) = 70\% \,\,\,\,\,\, \Rightarrow \,\,\,\,\,P\left( {{\text{not}}\,\,{\text{season}}\,\,{\text{raining}}} \right) = 30\%\)
\(20\% \,\,\mathop \to \limits^{\, + \,250\% } \,\,\,\underbrace {60\% + 10\% }_{300\% \,\left( {20\% } \right)\, + \,50\% \left( {20\% } \right)} = 70\% \,\,\,\,\,\, \Rightarrow \,\,\,\,\,\left\{ \matrix{\\
P\left( {{\rm{travel}}\,\,{\rm{when}}\,\,{\rm{season}}\,\,{\rm{raining}}} \right) = 20\% \hfill \cr \\
P\left( {{\rm{travel}}\,\,{\rm{when}}\,\,{\rm{not \,\,season}}\,\,{\rm{raining}}} \right) = 70\% \hfill \cr} \right.\,\,\)
\(?\,\, = \,\,70\% \cdot 20\% + 30\% \cdot 70\% \,\, = \,\,\underleftrightarrow {70\% \cdot \left( {20\% + 30\% } \right)}\,\, = \,\,\frac{1}{2}\left( {70\% } \right)\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,\left( {\text{C}} \right)\)
We follow the notations and rationale taught in the
GMATH method.
Regards,
Fabio.