Can you help me solve this geometric progression question?

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Robertwellson

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Can someone help me solve this? Geometric progression and show me the steps

A chemical reaction produces 25.6cm of chemical ' A ' in the first minute of the reaction. For each of the subsequent minute, the amount of chemical ' A ' produced reduce such that it form a geometric progression. Given that the total amount of chemical ' A ' produced if the reaction continue over a long period of time is 102.4cm

( a) Find the common ratio

( b) in which minute, the amount if chemical ' A ' produced is 8.1

Answer for a is 0.75

And b is 5
 
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If you have a GP where abs(r)<1, then the Sum to infinity = a/(1-r).

So you are given a, you are also given the sum to infinity, so you can work out r.

Give it a go and see if you get 0.75.

Then you should be able to work out (b).

Let us know how you go.
 
For a) you can use the formula of the sum of infinite terms(when r<1) and solve for r.
S=102.4. a=25.6
Once you have the ratio, you can use the general term formula to find n when the term is 8.1
 
Can someone help me solve this? Geometric progression and show me the steps

A chemical reaction produces 25.6cm of chemical ' A ' in the first minute of the reaction. For each of the subsequent minute, the amount of chemical ' A ' produced reduce such that it form a geometric progression. Given that the total amount of chemical ' A ' produced if the reaction continue over a long period of time is 102.4cm

( a) Find the common ratio

( b) in which minute, the amount if chemical ' A ' produced is 8.1

Answer for a is 0.75

And b is 5
 
Harry_the_cat said:
If you have a GP where abs(r)<1, then the Sum to infinity = a/(1-r).

So you are given a, you are also given the sum to infinity, so you can work out r.

Give it a go and see if you get 0.75.

Then you should be able to work out (b).

Let us know how you go.
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Thank you so much xD i got the answer
 
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