How to show 400 neutrinos are present?

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hraghav
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Homework Statement
Twelve electron neutrinos from SN 1987A were detected at Kamiokande in Japan. This
experiment consisted of a tank filled with 3x10^6 kg of water and surrounded by photomultiplier tubes to detect the Cerenkov radiation. Scale this to show that about 400 neutrinos could have been “seen” by humans, if we assume that eyeballs are composed primarily of water and weigh about 10 g each.
Relevant Equations
12/3*10^6 kg
4*10^-6 neutrinos * 0.01kg
Number of neutrinos detected per kg of water = 12/3*10^6 kg = 4*10^-6 neutrinos
Neutrinos detected by 1 eyeball = 4*10^-6 neutrinos * 0.01kg = 4*10^-8 neutrinos

I am not sure how to scale this to get 400 neutrinos. I did try multiple ways but either ended up with 3.69*10^9 or 4*10^-8 neutrinos. Could someone please help me with this. Thanks!
 
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