Aradioactive source has a half life of 80s.
how long will it take for 7/8 of the source to decay?

Lets make the original number of nuclides at the start is 100.

If 7/8 of 100 is decayed, that means 87.5 decayed.



And there is 1/8 left of the number of nuclide 100. Which is 12.5





How many Half lifes passed for 100 to become 12.5 is 3 Half-Lives.



Each Half-Life is 80 seconds so there is 240 seconds

The answer is that it takes 240 seconds.

Iread this book last year so take this with a grain of salt.gene jumps from the tree to compete with finny due to the fact that gene is always trying to do better than finny. he is put under the grasp of peer pressure due to finny almost forcing him to do this. ever since he first jumped finny kept pressuring him to jump since he thought gene enjoyed jumping.rather than uses this answer you should probably just reread chapters 3-4