Answer:
The rate of decrease is 8%
Step-by-step explanation:
we know that
The general equation for the radioactive decay can be written as:

where
a is the amount in kilograms after time t.
a_0 is the original amount of the substance or y-intercept of the function
r is the decay rate, written in decimals.
t is the time
In this problem we have

so

solve for r

Convert to percentage

The expression would be written as:

n-3
N is any number. This expression means two-fifths of a number, subtract three. Now substitute 25 for n.

(25)-3
=10-3
=7
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