C3 -#11, #40

[GuoQiang]

Hi, can any one shows me the solutions of #11 and #40? Thanks!

[Bama Gambler]

I'll do #40 because there is not a lot of symbols to write.

At time 0 you have 10,000 new lightbulbs.

At time 1 10% of those 10,000 have burned out. So you have 9,000 lightbulbs that are 1 year old, and 1,000 new bulbs that had to be replaced. Cost at time 1 = $1,000.

At time 2 30% of the 9,000 lightbulbs from time 1 burn out (2,700). You have to replace those 2,700 lightbulbs. Also, 10% of the 1,000 new lightbulbs from time 1 will burn out (100). You must replace those as well. At time 2 you replace 2700 + 100 = 2,800 lightbulbs. Total cost at time 2 = $2800. Also you have 9000 - 2700 = 6300 lightbulbs that are 2 years old. 1000 - 100 = 900 lightbulbs that are 1 year old. And of course, you have 2,800 new bulbs that you just replaced.

At time 3 50% of the 6300 bulbs that are 2 years old will burn out = 3150. Leaving you with 3150 bulbs that are 3 years old and still burning. 30% of the 1 year old bulbs will burn out = 270. Again leaving you with 630 2 year old bulbs. 10% of the new bulbs from time 2 will burn out leaving you with 2520 bulbs that are 1 year old. At time 3 you will have to replace 10,000 - 3150 - 630 - 2520 = 3,700. Cost at time 3 = $3,700.

Discount all the cost to time 0 and you get $6,688.26!

Hope this helps,
Bama Gambler

[GuoQiang]

Thanks Bama, how many questions you answered right?

[Bama Gambler]

Thanks Bama, how many questions you answered right?

I didn't "remember" (aka save) my answers. I did rework the test and for the most part was able to recall what I answered. I believe I got 31 right give or take 2.