see the plants grow in airthemetic progression.
day 1 its is 1 and day 2 it is 2, day 3 it is 4.......
so,
1,2,4,6,8,......
so it take 48 days to fill the pond..
total plants = 48/2(2*1+(48-1)*2)
total plants= 2304
so half the plants is 1152
so,
1152=n/2(2*1+(n-1)2)
n=47
it so 47 days to complete half the pond.
