If m, p, s and v are positive, and \(\frac{m}{p} <\frac{s}{v}\), which of the following must be between \(\frac{m}{p}\) and \(\frac{s}{v}\)
I. \(\frac{m+s}{p+v}\)
II. \(\frac{ms}{pv}\)
III. \(\frac{s}{v} - \frac{m}{p}\)
A. None
B. I only
C. II only
D. III only
E. I and II both
I.
\(\frac{m}{p}<\frac{s}{v} \to \frac{v}{p}<\frac{s}{m}\)
- manipulate to determine by adding p/p to left side and m/m to right side
\(\frac{v+p}{p}<\frac{s+m}{m} \to \frac{m}{p}<\frac{s+m}{v+p}\)
\(\frac{m}{p}<\frac{s}{v} \to \frac{m}{s}<\frac{p}{v}\)
- manipulate to determine by adding p/p to left side and m/m to right side
\(\frac{m+s}{s}<\frac{p+v}{v} \to \frac{m+s}{p+v}<\frac{s}{v}\)
I is always true.
II.
we know; \(\frac{m}{p}<\frac{s}{v} \) multiply both sides by \(\frac{m}{p} \)
=\((\frac{m}{p})^2<\frac{ms}{pv}\)
we know; \(\frac{m}{p}<\frac{s}{v} \) multiply both sides by \(\frac{s}{v} \)
=\(\frac{ms}{pv}<(\frac{s}{p})^2\)
combined
\((\frac{m}{p})^2<\frac{ms}{pv}<(\frac{s}{p})^2\)
squareroot
\(\frac{m}{p}<\sqrt{\frac{ms}{pv}}<\frac{s}{p}\)
it's not always true that
\(\sqrt{\frac{ms}{pv}} = \frac{ms}{pv}\)
hence II is not always true.
III.
let's start with the stem;
\(\frac{m}{p} <\frac{s}{v}\)
= \(0<\frac{s}{v} - \frac{m}{p} \)
= \(\frac{m}{p}-\frac{s}{v} <0 \)
= \(\frac{m}{p}-\frac{s}{v} < \frac{s}{v} - \frac{m}{p} \)
= \(\frac{2m}{p}-\frac{s}{v} < \frac{s}{v} \)
now lets evaluate III
if its between then that means
\(\frac{m}{p} < \frac{s}{v} - \frac{m}{p} <\frac{s}{v}\)
= add \(\frac{m}{p}\) and subtract \(\frac{s}{v}\)
= \(\frac{2m}{p}-\frac{s}{v} < \frac{m}{p} \)
therefore III is not inbetween. its less than.
so we know that its not always the case where
\(\frac{2m}{p}-\frac{s}{v} < \frac{m}{p} \)
based on our analysis of the stem it can be = \(\frac{m}{p} < \frac{2m}{p}-\frac{s}{v} < \frac{s}{v} \)