Decay contant of xenon and strontium

[cowboi123]

Homework Statement

The decay constant of xenon-142 is 0.462(s^-1), and the decay constant of strontium-90 is 7.85*10^-10 (s^-1). Initially, a sample of radioactive waste material contains equal numbers of strontium-90 and xenon-142 nuclei.

Calculate the time taken for the ratio: number of strontium-90 nuclei/number of xenon-142 nuclei to become equal to 1.20*10^6.

Homework Equations

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The Attempt at a Solution

Not sure, please help!

 

[ideasrule]

Have you seen the formula N=N0*e^(-kt)? Write out a formula for xenon, a formula for strontium, and a formula for the strontium:xenon ratio. The reason for doing this is that you know this ratio's numerical value and can set it equal to the formula.