the Ans is=
mp= 22.10^-6 kg
I hope it is helpful...
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Answer:
The time take is 
Explanation:
From the question we are told that
The decay constant is
The percentage fall is 
The equation for radioactive decay is mathematically represented as

Where is
is the new amount of the new the isotope while
is the original
At initial
% = 1
At
% = 0.80

=> 
=> 
Roughly 1609 meters in one mile
U=RI Ohm's law
then R=U/I
=120/0.08
=2250Ω
hope this helps you