The amount of radioactive material that would remain by the 7th hour of decay is 0.12 grams.
Exponential function
An exponential function is in the form:
y = abˣ
where y,x are variables, a is the initial value and b is the multiplicative factor.
Let y represent the amount of substance remaining after x hours. Hence:
a = 9375, at x = 4, y = 15:
15 = 9375(b)⁴
b = 0.2
y = 9375(0.2)ˣ
For the 7th hour, x = 7:
y = 9375(0.2)⁷ = 0.12
The amount of radioactive material that would remain by the 7th hour of decay is 0.12 grams.
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