Question

A scientist is measuring the amount of radioactive material in an unknown substance. When he begins measuring, there are 6.2 grams of radioactive substance. Twelve days later, there are 6.16 grams. After 19 days, there are 6.13 grams. After 46 days, there are 5.92 grams. Assuming that the decay is exponential, find the equation that determines the number of grams remaining after x days. Help!!!


A. y = 6(0.92)x
B. y = 6.15(0.98)x
C. y = 6.23(0.999)x
D. y = 6(0.999)x

Answer 1

@karatechopper

Answer 2

Any idea of where to start?

Answer 3

No clue honestly

Answer 4

are all these numbers being multiplied together or is there an exponent anywhere

Answer 5

Not that I can see.

Answer 6

This seems to be an exponential decay problem in which I woudl normally see "e" so I'm a bit lost here

Answer 7

I have found a formula - this should help:
The second formula down is what you should use.
I'll help you too.

Answer 8

ah so there is log and exponents

Answer 9

half life = elapsed time * log(2) / [log (bgng amt/ending amt)]
start 6.2 g
12 days 6.16 g

half life = 12 * .3010 / log (6.2 / 6.16)
half life =3.612 / 0.0028109773366
half life = 1,284.96 days

Let's see if that is correct
There's a half life calculator here:
http://www.1728.org/halflife.htm

Answer 10

Calculator says 1,285.1
For 19 days and 6.13 grams
half life = 1,160 days
For 46 days and 5.92 grams
half life = 690 days
something must be wrong with the data.
Is that typed correctly?

Answer 11

Hey welcome back!!

Answer 12

As far as the formula, I make it:
y = 6.2 * .99945^days

Answer 13

Is that problem stated without any typos?