Ratio methods keep track of changes in terms of the same unit.<br><br>
[[model:questions/solutions/q10431.png]]<br><br>
Let the number of boys = \(3u\) and girls = \(2u\).<br>
&bull; 40% of boys left, so boys remaining = 60% of \(3u = 0.6 \times 3u = 1.8u\)<br>
&bull; 25% of girls left, so girls remaining = 75% of \(2u = 0.75 \times 2u = 1.5u\)<br>
&bull; New ratio = \(1.8u : 1.5u = 1.8 : 1.5 = 18 : 15 = 6 : 5\)<br><br>
The new ratio of boys to girls is 6 : 5.<br>
Check: Boys: 3u → 1.8u (lose 1.2u). Girls: 2u → 1.5u (lose 0.5u). Ratio 1.8:1.5 = 6:5. ✓