A sample initially contains 4.4 moles of a radioactive isotope. How much of the sample remains after four half-lives?

0.275

Explanation:

Given that:

Initial number of miles of radioactive isotope = 4.4 moles

How much if the sample remains after 4 half life's

Half-life refers to the time taken by a sample to reduce to half of it's initial value.

After the first half life :

Initial / 2 = 4.4 / 2 = 2.2 moles

Second half life :

2.2 / 2 = 1.1 moles

Third half life :

1.1 / 2 = 0.55 Moles

Fourth half life :

0.55 / 2 = 0.275 moles

8 m/s because for him to get the same amount of energy as ray is putting out, bobby, who weighs half as much as ray, needs to run twice as fast.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.