Four rain-gauge stations A, B, C and D in a catchment area have recorded 20, 25, 22 and 15 cm respectively. If their Thiessen weights are 0.3, 0.4, 0.1 and 0.2, then what is the average depth of rainfall on the catchment?
1
19.2 cm
2
22.2 cm
3
21.2 cm
4
20.2 cm