SOLUTION: Isubmitted this one before and the person and I had two totally different answers. I asked the teacher and he gave me some choices to choose from. The diameter of the Milky Way di

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: Isubmitted this one before and the person and I had two totally different answers. I asked the teacher and he gave me some choices to choose from. The diameter of the Milky Way di      Log On

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Question 84488: Isubmitted this one before and the person and I had two totally different answers. I asked the teacher and he gave me some choices to choose from.
The diameter of the Milky Way disc is approximately 9 * 10^20 meters. How long does it take light, traveling at 10^16 m/year to travel across the diameter of the Milky Way?
The choices are 900,000 years, 90,000 years, 9,000 years and 900 years. Ihave to say that I was not evenclose soI am definitely doing something way wrong.Please help?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Since we're given a distance (the diameter of the galaxy) and a rate (the speed of light) and we want to find a time, we can use the distance-rate-time formula

d=rt where the distance (d) equals the rate (r) (or speed) multiplied by the time (t)

So let d=9%2A10%5E20 and r=10%5E16 and lets solve for t

9%2A10%5E20=%2810%5E16%29t Plug in d=9%2A10%5E20 and r=10%5E16

9%2A10%5E20%2F%2810%5E16%29=cross%28%2810%5E16%29%2F%2810%5E16%29%29t Divide both sides by 10%5E16 to solve for t

Now in order to reduce the left side 9%2A10%5E20%2F%2810%5E16%29, we can subtract the exponents.

9%2A10%5E%2820-16%29=t Subtract the exponents using the identity x%5Ea%2Fx%5Eb=x%5E%28a-b%29

9%2A10%5E4=t

9%2A10000=t

90000=t

t=90000

So it takes light 90,000 years to travel the diameter of the Milky Way.