Stuck on an urgent Maths GCSE q- can anyone help please?

[Proud_Dad]

Because the question states that the population decreases exponentially I would have thought you would need to use 'e' and would have used the exponential growth/decay equation.

i.e. N(t) = N(0).e^(xt)

where x is the growth/decay constant and t is the time interval. First work out x using the decay between 5 and 7 weeks (t = 2), and then use that for 2 to 5 weeks (t = 3).

Is that something they would know about at GCSE though, or is that more of an A level topic?

[Guest55]

That was what I would have assumed but e is not on the GCSE syllabus - hence my initial query.

It is general growth/decay they mean - it does say 'exponential' in the syllabus which is confusing.

[Proud_Dad]

That was what I would have assumed but e is not on the GCSE syllabus - hence my initial query.

It is general growth/decay they mean - it does say 'exponential' in the syllabus which is confusing.

Hey, just worked out the numbers and your method using sqrt (3/4) and my method using 'e' both give EXACTLY the same answer, 1847.52!

I'm sure there's a good reason for that but its a bit beyond me! Interesting though isn't it!

[Guest55]

I'd be worried if they didn't but the mark scheme does not include 'e' at all ....

[Kit]

Guest 55 - DD was very happy coming out of her Maths exam today- this type of problem came up apparently and this time she knew exactly how to tackle it. Thanks again!

[Guest55]

That's great I hope there was no animal cruelty this time.

I'll have access to the paper soon when is uploaded to the Edexcel teacher website.

[Kit]

Not unless bacteria count

[Kit]

A postscript- thank you for your help, particularly G55, DD was very happy with her Maths GCSE result

[booellesmum]

DD is just doing this as a practice question.
This thread came up when we googled- very helpful, thank you!