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# Magic Penny Parable

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Suppose you stacked pennies after 22 days. How high would the stack rise, in kilometers?

Guest Mar 13, 2017
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#1
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Suppose you stacked pennies after 22 days. How high would the stack rise, in kilometers?

I assume you mean you stack 1 penny the first day, add 2 the second day, add 4 the third day.  etc

$$1+2+4+ .... 2^{k-1}.........+ 2^{22-1}\\ \boxed{S_n=\frac{a(r^n-1)}{r-1}}\\ S_n=\frac{1(2^{22}-1)}{2-1}\\ S_n=2^{22}-1\\$$

I found this on the web i assume it means a penny is 1.52mm thick.

The United States one- cent coin oft called penny , is a unit of currency equaling ... The coin is 0.75 inches (19.5 mm) in diameter and 0.0598 inches (1:52 mm) in thickness .

((2^22-1)*1.52)/(1000*1000) = 6.37534056

So that is approximately 6.4 kilometres

Melody  Mar 13, 2017
#2
+32
+5

2x22=44

44x1.52=1672/25

1672/25=66.88 Milimeters

66.88 mm= 0.00006688 Km

ZerpMerp  Mar 13, 2017

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