Two vases are cylindrical in shape.
The larger vase has diameter 20 cm.
The smaller vase has diameter 10 cm and height 16 cm.
The larger vase is partially filled with water.
Then the empty smaller vase, with the open end at the top, is slowly pushed down into the water, which flows over its rim.
When the smaller vase is pushed right down, it is half full of water.
What was the original depth of the water in the larger vase?
This problem is taken from the UKMT Mathematical Challenges