What is the half-life of proton decay in order to detect 3 decays in one year?

[Granger]

Assume you want to find experimental evidence of the proton decay. For this, you use a cylindrical tank with 36 meters high and 17 meters radius which is full of water (18 g / mol). Around the tank are detectors whose overall detection efficiency of a proton decay that gives within the deposit is 20%.Admitting that collaboration has operated the device for an effective period of one year, where the average life than the proton should have for that period had been possible to detect 3 decays?I'm not understanding what they mean with "3 decays"... Like 3 half-lives?
The correct answer is 7.3 x 10^32 years...

 

[jbriggs444]

I'm not understanding what they mean with "3 decays"... Like 3 half-lives?

"detect 3 decays" = 3 protons have decayed and had those decays detected.

 

[SteamKing]

Assume you want to find experimental evidence of the proton decay. For this, you use a cylindrical tank with 36 meters high and 17 meters radius which is full of water (18 g / mol). Around the tank are detectors whose overall detection efficiency of a proton decay that gives within the deposit is 20%.Admitting that collaboration has operated the device for an effective period of one year, where the average life than the proton should have for that period had been possible to detect 3 decays?I'm not understanding what they mean with "3 decays"... Like 3 half-lives?
The correct answer is 7.3 x 10^32 years...

No. Inside that tank full of water, you have a huge number of protons. The purpose of the experiment is to detect when a proton decays. The half-life of proton decay is an amount of time so immense, its value is thought to exceed the age of the universe by many orders of magnitude.

I believe what the question is asking, is to calculate the half-life period of proton decay such that this experiment would detect the decay of 3 individual protons in the course of a year's time.