| Exam Board | OCR |
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| Module | Further Pure Core 1 (Further Pure Core 1) |
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| Year | 2018 |
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| Session | March |
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| Topic | First order differential equations (integrating factor) |
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9 In an experiment, at time \(t\) minutes there is \(Q\) grams of substance present.
It is known that the substance decays at a rate that is proportional to \(1 + Q ^ { 2 }\). Initially there are 100 grams of the substance present and after 100 minutes there are 50 grams present.
Find the amount of the substance present after 400 minutes.