The salt content of the Caspian sea is 0.13 kg for every liter of water. How many kg of salt are in 70 liters?

Question

Word Problem

Answer 1

Set up a proportion.

 

The word "for" or the word "per" indicates a fraction.  "0.13 kg salt for 1 L water" is   0.13 kg / 1 L.

 

At the same rate, there is x (unknown) kg salt for 70 L water.  That is,  x kg / 70 L.

 

Set these equal:

     0.13 kg / 1 L  = x kg / 70 L

 

Cross-multiply:

     1x = 0.13*70

        x = 9.1

Answer 2

You are given that there are 0.13 kg salt per liter of water - this is a relationship between the salt and the seawater. We can say that 0.13 kg = 1 L seawater. Even though these quantities aren't identical they can be considered equivalent for the purposes of this specific situation, because if you have 1 L of this sea water, then you will have 0.13 kg salt in it!

 

This becomes a simple conversion, where we can start with 70 L seawater and then multiply it by a conversion factor:

 

70 L seawater x (^{0.13 kg salt}/_{1 L seawater}) = 9.1 kg salt

 

Notice that the units "L seawater" cancel out here. ;)

 

Hope that helps. :)