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I have no idea how to solve part (a) or (b). Any help?

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Sir Cumference
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(Original post by MainlyMathsHelp)
I have no idea how to solve part (a) or (b). Any help?
This is a new topic for GCSE but I'm finding that it's not being taught well / at all in schools.

Firstly, if you don't already know, a geometric progression/sequence is a sequence where to get from one term to the next you need to multiply by a number. This is different to an arithmetic sequence where you add to get from one term to the next.

E.g. 2, 4, 8, 16, 32,...

This is a geometric sequence where the ratio between terms (the multiplier) is equal to 2.

This sequence has nth term 2^n

In general, a sequence with first term a and ratio r has nth term ar^{n-1}.


To show that a sequence is geometric, you just need to show that there is a constant ratio between terms.

So for part a), first write out the sequence and then explain that the ratio is constant. E.g. the first term will be 1000.

Have a go at that and post your ideas if you get stuck.

If you're familiar with compound interest, then you'll find that part b) can be done in a very similar way.
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PersonInProgress
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(Original post by notnek)
This is a new topic for GCSE but I'm finding that it's not being taught well / at all in schools.

Firstly, if you don't already know, a geometric progression/sequence is a sequence where to get from one term to the next you need to multiply by a number. This is different to an arithmetic sequence where you add to get from one term to the next.

E.g. 2, 4, 8, 16, 32,...

This is a geometric sequence where the ratio between terms (the multiplier) is equal to 2.

This sequence has nth term 2^n

In general, a sequence with first term a and ratio r has nth term ar^{n-1}.


To show that a sequence is geometric, you just need to show that there is a constant ratio between terms.

So for part a), first write out the sequence and then explain that the ratio is constant. E.g. the first term will be 1000.

Have a go at that and post your ideas if you get stuck.

If you're familiar with compound interest, then you'll find that part b) can be done in a very similar way.
See I did write them out and found there was no geometric progression so I must have done something wrong (I photoshopped my working out because I wasn't sure if it was right). So I did 1000 x 1.5^0 = 1000 and then I increased the power by 1 for the second day etc. My results were 1000, 1500, 2250, 3375 and 5062.5. Have I made a mistake?
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Sir Cumference
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(Original post by MainlyMathsHelp)
See I did write them out and found there was no geometric progression so I must have done something wrong (I photoshopped my working out because I wasn't sure if it was right). So I did 1000 x 1.5^0 = 1000 and then I increased the power by 1 for the second day etc. My results were 1000, 1500, 2250, 3375 and 5062.5. Have I made a mistake?
No you haven't made a mistake. Each term is the previous term multiplied by 1.5.
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