Asample of a radioactive material decays over time.
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D  10 is the size of the sample at the time it was discovered

Step-by-step explanation:

An exponential equation is written in the form

y = ab^x

where a is the initial value

b is  the growth or decay

x is the amount of time

y = 10 (.5)^x

10 is the initial value

.5 is how fast it is decaying (50 % decay rate)

x is the time in days