If you stacked Avogadro's number of pennies one on top of the other on Earth's surface, how far would the stack extend (in km) ? [For comparison, the sun is about 150 million km from Earth and the nearest star (Proxima Centauri) is about 40 trillion km from Earth.]

the length of pennies will be like the Proxima Centauri

Explanation:

50 pennies make the length of a meter, so:

50 pennies = 1 m

x = 1 km

x = (50 x 1000) = 50 000 pennies = 1 Km

Then if the Avogadro's number is 6.022 x 1023 so:

50 000 pennies = 1 km

6.022 x 1023 pennies = x

x = (6.022 x 1023 / 50 000) = 1.2044 x 1019

This big number is closer to the 40 trillion km of the Proxima Centauri.

Hope this answer is useful.