Start with the ratio and track the changes using units.<br><br>
[[model:questions/solutions/q10433.png]]<br><br>
Let chickens = \(4u\) and ducks = \(3u\).<br>
&bull; After 25% of chickens were sold: chickens remaining = 75% of \(4u = 3u\).<br>
&bull; After 50% more ducks were bought: ducks after = 150% of \(3u = 4.5u\).<br>
&bull; Total birds = \(3u + 4.5u = 7.5u = 390\).<br>
&bull; \(u = 390 \div 7.5 = 52\).<br>
&bull; Chickens at first = \(4u = 4 \times 52 = 208\).<br><br>
There were 208 chickens at first.<br>
Check: Chickens = 208, ducks = 156. After: chickens = 156, ducks = 234. Total = 390. ✓