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**My heads spinning help!!**

As usual ive left my work to the end of the holiday and after 2 hours of physics questions my head is in a spin... i have a cou[ple of simple quetions where i know the soluion isobvious but i cant get my had around the answers... would anyone be able to point me in the right direction so i can answer them?

Changes in exponential:

1) how wold i go about working out the probability of decay of a substance in 1 second.I have been given a half life and a decay rate.

Spring constants:

2) I have been given the mass of a spring and the time for oscillations --> how do i work out the spring constant? I know f=kx but i am really confused

Thanks :)