Posted by **trace** on Thursday, September 16, 2010 at 4:40pm.

assume the half-life of the substance is 31 days and the initial

amount is 183.9 grams.

(a) Fill in the right hand side of the following equation which expresses

the amount A of the substance as a function of time t (the coefficient of t in the exponent should have at least four significant digits):

(b) When will the substance be reduced to 2.4 grams?

(use decimals.)

- calculus -
**drwls**, Thursday, September 16, 2010 at 7:33pm
There is not "followiong equation" to fill in.

Amount left = 183.9*2^(-t/31)

You don't need 4 sig figs in the exponent in this form if the half life is exactly 31 days.

(b) When amount left = 2.4,

2.4/183.9 = 0.01088 = 2^(-t/31)

-4.5212 = (-t/31)*ln 2 = -0.02236t

t = 202.2 days

- calculus -
**annonymous**, Thursday, September 16, 2010 at 8:06pm
the second answer is 194.052 days

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