The Des Plaines River Bridge is 2.1 km long. Engineers are considering re-lighting the bridge with a pole placed every 120 feet of the bridge length starting from the south end. Each pole will support four light globes. How many globes will be required for the re-lighting project?
Can someone help me set this problem up, please?

Question

The Des Plaines River Bridge is 2.1 km long. Engineers are considering re-lighting the bridge with a pole placed every 120 feet of the bridge length starting from the south end. Each pole will support four light globes. How many globes will be required for the re-lighting project?
 Can someone help me set this problem up, please?

anonymous · Answer

Unit conversions again, my friend.
1 mi = 1.60934 km = 5280 ft

anonymous · Answer

Once you have the span of the bridge in feet, it's simply a matter of finding how many poles to put up, then finding how many lights for that amount of poles.

anonymous · Answer

Or...in other words:
2.1 km * 1mi/1.60934km * 5280ft/mi = 6889.781ft /120ft = 57.41 poles (round down, you can't really have .41 of a pole)

57*4 = 228 bulbs

anonymous · Answer

I must have been going out too far on my decimal points because for the last couple of days I have been getting 229.6 bulbs.

anonymous · Answer

Thank you , again!

anonymous · Answer

229.6 is the computational answer, but makes no sense given the context of the problem (as you cannot have .6 of a bulb). If you leave it at 229 bulbs, that means you built 57 and a quarter poles, which also doesn't make sense, so I just rounded down to 228.

Happy to help!

anonymous · Answer

I'm so used to my professors telling me to go out to as many decimal places that the calculator will give me.  So that was my mistake.