Let the rock’s height be R and the cat’s height be C.
The first picture shows the difference between their heights:
R − C = 100
The second picture shows their combined height:
R + C = 160
Add the two equations:
2R = 260
So the rock is 130 cm tall. Substitute that into the second equation:
130 + C = 160
C = 30
Therefore, the cat is 30 cm tall. The common mistake is treating the first measurement as the rock’s height instead of the difference between the rock and cat.


