### Home > CCA2 > Chapter 6 > Lesson 6.1.5 > Problem6-77

6-77.

The half-life of an isotope is 1000 years. A 50-gram sample of the isotope is sealed in a box.

1. How much is left after 10,000 years?

Half-life means time in which half of the original 50 grams will remain.

y = abn

a is the initial value,
b is the multiplier (0.5 since we are working with a half-life),
n is the number of thousands of years, and
y is the amount of the isotope that remains (in grams).

The equation is y = 50(0.5)x. Substitute 10 for x.

Use the equation below, where x is the number of years.

$y = 50(0.5)^{\frac{x}{1000}}$

2. How long will it take to reduce to 1% of the original amount?

Use the equation from the help for part (a).
In this case, y = 1% of 50 and you are solving for x.

≈ 6600 years

3. How long will it take until all of the original sample of the isotope is gone? Support your answer.

$0=50\left( \frac{1}{2}\right) ^x$