Seeing their color and dandy color (say white) Andy guess his color that remains - red.
Brandy sees Dandy has white. Knows Andy has red. Sees candy has blue. Knows she has blue also.
Candy sees dandy white. Knows Andy red. Knows brandy blue. Knows himself blue.
Dandy now knows all colors of rest. And picks white that is left.
All the other three are multiples of bottom number so answer is 9. An tukka also works here. If we add other three numbers and neglect zero ie first digit then answer is bottom number.
Anyways
Solution
add the above numbers and divide the total sum by 10. like
no:1 (12+18+30)/10= 6
No:2(16+24+40)/10=8
No:3 (45+18+17)/10=9 @Anjul sun moves ..
Next
What goes up and down, but still remains in the same place?