# Sonali decided to do a survey of birds in her garden over an hour...................how many blue tits did Sonali count?

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Sonali decided to do a survey of birds in her garden over an hour.
In that time there were two more sparrows than blue tits, of which there were twice as many as robins, of which there were 80% fewer than the number of wagtails observed.
If these were the only species of bird present, and there was an average of eight birds of each species, how many blue tits did Sonali count?

posted Jun 8, 2019

8

Sparrow- s
Tit- t
Robin- r
Wagtail- w

s=t+2
r=s/2= 1/2*(t + 2)
r=w-80%---> w=1.8*r=1.8*1/2*(t+2)
t+s+r+w=4*8=32 --->
---> t+(t+2)+t/2+1+1.8*1/2*(t+2)=32 --->
---> t=8, s=10, r=5, w=9
Blue tits counted - 8

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