Can't get the right answer

[esig]

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

[imatfaal]

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)

[esig]

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?

[imatfaal]

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.