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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s