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Mathematics 20 Online
OpenStudy (katecc379):

Christina bought a yoyo from a company that claims that, with each retraction, the string rolls up by 70% of the original length. She sets up a tape measure and throws the yoyo 3 times. Her data are charted below.

OpenStudy (katecc379):

OpenStudy (lord_box):

This is a geometric series.\[a_n = a_1*r ^{n-1}\]

OpenStudy (lord_box):

where a_1 is the initial term, 3, and r is the common ratio, 0.7.

OpenStudy (lord_box):

this is the formula for a sum of a geometric series:\[S_n = \frac{ a_1(1-r^n) }{ 1-r }\]

OpenStudy (faiqraees):

Use the formula \[\large\rm Sum=\frac{initial(1-(\frac{rate}{100})^{times}) }{1-(\frac{rate}{100})}\]

OpenStudy (katecc379):

what is r

OpenStudy (lord_box):

r is the rate, which is 0.7, since it becomes 70% shorter.

OpenStudy (katecc379):

then what is the times

OpenStudy (lord_box):

times is the number of throws.

OpenStudy (katecc379):

so 10?

OpenStudy (lord_box):

yes

OpenStudy (katecc379):

that gave me 3.02 which isn't an option

OpenStudy (faiqraees):

initial is 3 Rate is 70/100 Times is 10 Try again using these values

OpenStudy (lord_box):

You divided the rate 0.7 by 100. 0.7 is already divided by 100.

OpenStudy (katecc379):

wait np 9.72?

OpenStudy (faiqraees):

Correct

OpenStudy (katecc379):

you guys rock

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