esig Posted November 18, 2014 Share Posted November 18, 2014 I have a problem and I have the answer and the method in the book but when in put it in the calculator or excel or google I get the wrong answer The problem is An average family f four uses roughly 1200 liters of water per day. One liter =1000cm3 How much depth would a lake lose per year if it uniformly covered an area of 50 square km and supplied a local town with a population of 40000 people? Consider only population uses and neglegt evaporation and so on So I started my calculation and according to the book I did them right but my answer is not right. 40000 people(1200 L/d/4 people)(365 days/1 yr)(1000cm3 /1 L)(1km/10^5 cm) My calculation= 43 800 000 Books= 4.4*10^-3 I maybe thought that mine was in cm since the book gives it answer in km but if I did my conversion right I have 438 km and the books is 0.0044 km Can somebody tell what it is I am doing wrong? I took a screen shot of the books solution Link to comment Share on other sites More sharing options...
imatfaal Posted November 18, 2014 Share Posted November 18, 2014 I have a problem and I have the answer and the method in the book but when in put it in the calculator or excel or google I get the wrong answer The problem is An average family f four uses roughly 1200 liters of water per day. One liter =1000cm3 How much depth would a lake lose per year if it uniformly covered an area of 50 square km and supplied a local town with a population of 40000 people? Consider only population uses and neglegt evaporation and so on So I started my calculation and according to the book I did them right but my answer is not right. 40000 people(1200 L/d/4 people)(365 days/1 yr)(1000cm3 /1 L)(1km/10^5 cm) My calculation= 43 800 000 Books= 4.4*10^-3 I maybe thought that mine was in cm since the book gives it answer in km but if I did my conversion right I have 438 km and the books is 0.0044 km Can somebody tell what it is I am doing wrong? I took a screen shot of the books solution 42.png You have converted cm to km (ie factor of 100,000) - to convert cm^3 to km^3 you need to cube the conversion factor as well and when you do the second part with the lake remember than km^2 to cm^2 is a conversion factor that must be treated similarly (although not identical) Link to comment Share on other sites More sharing options...
esig Posted November 18, 2014 Author Share Posted November 18, 2014 I am sorry but english is not my first language, what do you mean by that I need to cube the conversion factor as well? Link to comment Share on other sites More sharing options...
imatfaal Posted November 18, 2014 Share Posted November 18, 2014 Think about it first with converting cm to m - the numbers are easier. There are one hundred centimetres in a metre. How many cm^2 are there in a m^2? and in a m^3? By the way for those not English native speakers - cube in these circumstances means raise to the power of three. Link to comment Share on other sites More sharing options...
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