The probability that the annual maximum flood discharge will exceed $25000 \mathrm{~m}^{3} / \mathrm{s}$, at least once in next 5 years is found to be $0.25 .$ The return period of this flood event (in years, round off to 1 decimal place ) is
The probability that the annual maximum flood discharge will exceed $25000 \mathrm{~m}^{3} / \mathrm{s}$, at least once in next 5 years is found to be $0.25 .$ The return period of this flood event (in years, round off to 1 decimal place ) is