1) C
Let us use numbers instead of the ratio.
Let us say there are 80 birds and 1 persons on the island.
Let population of seabirds 20 years ago = ‘s’
Let population of people 20 years ago = ‘p’
s – 60%(s) = 80
p + 25%(p) = 1
s – 0.6s = 80
p + 0.25p = 1
s (1-0.6) = 80
p (1+0.25) = 1
0.4s = 80
1.25p = 1
s = 200
p = 0.8
Ratio = 200 : 0.8
We need to increase the ratio of persons to 1.
0.8 + 25% = 1
We increased 0.8 by 25%. Hence we also need to increase 200 by 25%. This equates to 250.
Hence the ratio is 250 : 1. The answer is C.
