Applications of Series Q (1 Viewer)

[Smile12345]

Hello All

Could someone please help me with the following question:

"Water evaporates from a pond at an average rate of 7% each week."

"What percentage is left after 15 weeks?"

Thanks for your help in advance.

Cheers
Smile

 

[Smile12345]

Please.

 

[Kurosaki]

Hello All

Could someone please help me with the following question:

"Water evaporates from a pond at an average rate of 7% each week."

"What percentage is left after 15 weeks?"

Thanks for your help in advance.

Cheers
Smile

I'll take a stab- so 7% of the water evaporates every week. This means after every week, only 93% of the water originally there remains.
Let the amount of water be M.
Water after:
0 weeks - M
1 week- 0.93 M
2 weeks -
...
15 weeks
Thi9s gives us 0.3367M more or less, so there is about 33.67% of the water remaining?

 

[Smile12345]

I'll take a stab- so 7% of the water evaporates every week. This means after every week, only 93% of the water originally there remains.
Let the amount of water be M.
Water after:
0 weeks - M
1 week- 0.93 M
2 weeks -
...
15 weeks
Thi9s gives us 0.3367M more or less, so there is about 33.67% of the water remaining?

Thanks very much... Interesting way to do it... You're correct.
+1

 

[Smile12345]

How about this.... I think it's similar....

'A 100m cliff erodes by 2/7 of its height each year.

What will the height of the cliff be after 10 years?'

Thanks for your assistance in advance.

 

[seanieg89]

How about this.... I think it's similar....

'A 100m cliff erodes by 2/7 of its height each year.

What will the height of the cliff be after 10 years?'

Thanks for your assistance in advance.

You should try this yourself and post your attempt up, it is exactly the same question with different numbers.

 

[Smile12345]

Sorry, I just can't get it.... I've tried multiple ways, multiple times but not working.............

 

[seanieg89]

Sorry, I just can't get it.... I've tried multiple ways, multiple times but not working.............

For the same reason as in the previous question, you are multiplying by a factor of 1-2/7 = 5/7 each year, so the answer is:



Chuck it into a calculator to get an answer however accurate you like.

 

[Smile12345]

For the same reason as in the previous question, you are multiplying by a factor of 1-2/7 = 5/7 each year, so the answer is:



Chuck it into a calculator to get an answer however accurate you like.

Thanks...

But with the other one, if I'd done that...



I don't think this is right...........

Probably confusing myself.

 

[seanieg89]

Thanks...

But with the other one, if I'd done that...



I don't think this is right...........

Probably confusing myself.

Because you are not starting with 100 and units aren't specified in the first question. The first question is just asking the proportion...which is (0.93)^15. The idea is exactly the same though, of multiplying by a fixed factor for each unit of time.

 

[Smile12345]

Because you are not starting with 100 and units aren't specified in the first question. The first question is just asking the proportion...which is (0.93)^15. The idea is exactly the same though, of multiplying by a fixed factor for each unit of time.

Thanks Seanieg...

 

[Danneo]

4 years late but its 100*(5/7)^9 since geometrical formula is ar^n-1
Answer should be 4.84m
Cheers, flies away to the present