Question

An original sample of K-40 has a mass of 25.00 grams. After 3.9 × 109 years, 3.125 grams of the original sample remains unchanged. What

is the half-life of K-40?
(1) 1.3 × 109 y (3) 3.9 × 109 y
(2) 2.6 × 109 y (4) 1.2 × 1010 y

Answer 1

`(25)/(3.125)=8=2^3\\\\(3.9*10^9)/(3)\\1.3*10^9`

(1) 1.3*10^9 years

Answer 2

La respuesta correcta es
`1.3*10^(9)`

Step-by-step explanation:

Hello! Let's solve this!

First we have to know the mass / mass exponent without changes

The data is:

m = 25 g

mc (mass without changes) = 3.125g

25 / 3,125 = 8 =
`2^(3)`

The exponent is 3, so we divide the number of years by three.

`(3.9*10^(9) )/(3)`

La respuesta correcta es
`1.3*10^(9)`