Arithmetic and geometric progression: Tin ore is extracted from a certain mine....

[cai cen ho]

Can anyone help with the question no.10?..which cause me a big problem...i hav totally no idea to solve it...

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[Deleted member 4993]

Can anyone help with the question no.10?..which cause me a big problem...i hav totally no idea to solve it...

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Please put your attachment in a "readable" orientation.

 

[tkhunny]

Decrease of 10% = Multiply by 1 - 0.10 = Multiply by 0.90

 

[stapel]

For those who don't want to try to peer sideways, the exercise in question reads as follows:

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Tin ore is extracted from a certain mine. During the first year of production, a yield of 8,000 kilograms of ore was obtained. With the increasing difficulty of mining, the production of tin ore each subsequent year shows a decrease of 10% on the previous year's production.

Assuming that mining continues in the same way for an indefinite period of time, calculate the maximum amount of tin ore which could be probably extracted.

For economic reasons, mining is abandoned once the annual output of tin ore falls below 1,000 kilograms. Calculate:

(a) the number of years the mine is in operation,
(b) the total pro0duction of tin ore during this time, and
(c) the percentage of tin ore not extracted from this mine.

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From the subject line, it should probably be assumed that the original poster is expected to use a summation of some sort in order to answer these questions.

 

[mmm4444bot]

[I have] totally no idea [how] to solve it …

Have you studied Geometric Progressions and how to sum a beginning number of terms in such a progression?

tkhunny gave you a good hint: If 8000 decreases by 10%, then it becomes (0.9)(8000). Think about what happens, when this new amount decreases by 10%. How would you express the result?

Also, I'm not sure how we can express the amount of ore left in the mine, as a percentage of some whole, without knowing the whole. They seem to be asking for a percentage of ore weight in the mine before extraction began, but I'm not sure.