mech

Let the drops fall after a time interval 't' before the successive drop.

Let drop 1 be now falling. Then drop 2 will have travelled for 't', drop 3 for '2t' and drop 4 for '3t'

S1 (dist of 2 from roof) = 0.5gt²
S2 (dist. between 2 and 3) = 0.5g(2t)²-0.5gt² = 3*0.5gt²
S3 (dist. between 3 and 4) = 0.5g(3t)²-0.5g(2t)² = 5*0.5gt²

So, S1:S2:S3 = 1:3:5