Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge / 2011 / Paper 1 / 12 / e / Solution

On interrupted outcomes, $r=S-T$; on the other outcomes the sentinel value is negative and cannot exceed $r_0>0$. ConsequentlyOn the diagram in part (b), this is the first-quadrant region below $t=s-r_0$, starting at the horizontal intercept $s=r_0$. It lies strictly inside the interruption region $t<s$.