### Home > A2C > Chapter 7 > Lesson 7.2.4 > Problem 7-146

7-146.

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

*y* = *ab ^{n}*

*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.

Use the equation from the help for part (a).

In this case, *y* = 1% of 50 and you are solving for *x*.

≈ 6600 years