If her lunch <em>cost</em> $9.80 and she left a $1.47 <em>tip</em>, if we do <u>$1.47/ $9.80 = 0.15. </u> So 15% is our percent of tip.
(That is the <em>cost</em> of the first day and the <em>tip</em> of the second day divided.) If we want to find out how much her next<em> tip</em> should be, we have to multiply the percent of tip (15%) with the next days <em>cost </em>($12.60.) So, <u>$12.60 * 15%= $1.89 </u>