# math

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent.
a)(a) What is the half-life of the element? half-life:
b)How long will it take for a sample of 100 mg to decay to 51 mg?
time needed:

1. 👍
2. 👎
3. 👁
1. .36 = (1/2)^(100/k)
k = 67.84

so, the half-life is 67.84 days
Makes sense, since the sample has decreased by a little more than 1/2 in 100 days.

51/100 = (1/2)^(t/67.84)
t = 65.9 days

1. 👍
2. 👎
2. GREETINGS

1. 👍
2. 👎
3. no

1. 👍
2. 👎

## Similar Questions

Which of the following statements about radioactive dating is true? a. Radioactive decay is the rate at which new atoms form. b. During radioactive decay, atoms break down, releasing particles or energy. c. The rate of decay of a

2. ### chemistry

The half-life for the radioactive decay of calcium-47 is 4.5 days.If a sample has an activity of 4.00uCi after 13.5 days, what was the initial activity of the sample?

3. ### Calculus-Modeling Equations

An unknown radioactive element decays into non-radioactive substances. In 420 days the radioactivity of a sample decreases by 39 percent. 1.What is the half-life of the element? 2.How long will it take for a sample of 100 mg to

4. ### Calculus

The radioactive element polonium decays according to the law given below where Q0 is the initial amount and the time t is measured in days. Q(t) = Q0 · 2-(t/140) If the amount of polonium left after 700 days is 45 mg, what was

1. ### Math

A radioactive substance decays exponentially. A scientist begins with 130 milligrams of a radioactive substance. After 20 hours, 65 mg of the substance remains. How many milligrams will remain after 24 hours?

2. ### College algerba

The​ half-life of a certain radioactive element is about 1500 years. After 2800 ​years, what percentage P of a sample of this element​ remains?

3. ### Science

I'm kinda in a rush but take your time!Thx! 1.What was Henri Becquerel studying when he accidentally discovered radioactivity? A.photography B.properties of black light C.properties of X-rays D.solar energy 2.When Marie Curie

4. ### Algebra 2

A particular radioactive element has a half life of 10.0 days. How much is left after 30.0 days if the sample started with 345g?

1. ### Math

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a

2. ### Physical Science- Help Please!

Suppose that you are given a 100 gram sample of a radioactive substance with a half-life of 32 days. How many grams will be left after 192 days?

3. ### Calculus

A certain radioactive material decays exponetially. The percent, P, of the material left after t years is given by P(t)= 100(1.2)^-t a)Determine the half life of the substance

4. ### Chemistry

As a sample of the radioactive isotope 131 I decays, its half-life a)decreases b)increases c)remains the same