Let the opening price on Monday = \(o\)
First it went up by \(x\)% and then went down by \(y\)%:
\(o[(1+\frac{x}{100})(1-\frac{y}{100})]\)
\(o[1+\frac{x}{100}-\frac{y}{100}-\frac{xy}{10000}]\)
The share price will be higher on Tuesday than the opening price on Monday if \(\frac{x}{100}-\frac{y}{100}\)is greater than \(\frac{xy}{10000}\)
(1) x>yLet the cost of the share on Monday = \(50\).
[Case 1] x = 100 and y = 10: Closing price on Monday:\(50*(1+\frac{100}{100}) = 100\), closing price on Tuesday: \(100*(1-\frac{10}{100}) = 90\). In this case the price on Tuesday is greater.
[Case 2] x = 100 and y = 50: Closing price on Monday:\(50*(1+\frac{100}{100}) = 100\), closing price on Tuesday: \(100*(1-\frac{50}{100}) = 50\). In this case the price on Tuesday is the same as Monday.
INSUFFICIENT(2) x−y>xy/100Taking \(x−y>\frac{xy}{100}\) and multiplying through by \(\frac{1}{100}\) gives: \(\frac{x−y}{100}>\frac{xy}{10000}\)
This is identical to what one finds in \(o[1+\frac{x}{100}-\frac{y}{100}-\frac{xy}{10000}]\).
As \(\frac{x}{100}-\frac{y}{100}\) is greater than \(\frac{xy}{10000}\); subtracting \(\frac{xy}{10000}\) from \(\frac{x}{100}-\frac{y}{100}\), adding \(1\) and then multiplying that through by \(o\) can only result in a value greater than \(o\). Therefore, the price of the share at the end of Tuesday will be greater than the share's opening price on Monday.
SUFFICIENT
ANSWER B