An object weigh 40N in air ,weigh 20N when submerged in water, and 30N when submerged in a liquid of unknown liquid density. what is the density of unknown of liquid?

The density is  

Explanation:

From the question we are told that

    The weight in air is  

     The weight in water is  

     The weight in a unknown liquid is  

Now according to Archimedes principle the weight of the object in water is mathematically represented as

Where   is he mass of the water displaced

 substituting value

Now according to Archimedes principle the weight of the object in unknown  is mathematically represented as

Where   is he mass of the unknown liquid  displaced

 substituting value

dividing equation 2 by equation 1

=>  

Now since the volume of water and liquid displaced are the same then

This because

So if  volume is constant

         mass = constant * density

Where is the density of the liquid

     and   is the density of water which is a constant with a value

So

connect the batteries in series and hope

answer and explanation;