Thread: rate problem with separation of variables

The rate at which a substance dissolves in a solution is proportional to the amount of the substance that is present. Thirty grams of sodium chloride are put in a litre of water , and is found that 1 hr later only 10g are left. How much will be left after 30min?

i have no idea how to do this!

Originally Posted by shawli

The rate at which a substance dissolves in a solution is proportional to the amount of the substance that is present. Thirty grams of sodium chloride are put in a litre of water , and is found that 1 hr later only 10g are left. How much will be left after 30min?

i have no idea how to do this!

The rate of change of the substance is porportional to the amount of the substance. The instantanous rate of change in the derivitive. Use this to work out what the feunction for N is. Then input your numbers.

Originally Posted by shawli

The rate at which a substance dissolves in a solution is proportional to the amount of the substance that is present. Thirty grams of sodium chloride are put in a litre of water , and is found that 1 hr later only 10g are left. How much will be left after 30min?

i have no idea how to do this!

The rate of change of the substance is proportional to the amount of the substance. The instantaneous rate of change in the derivative. Use this to work out what the function for N is. Then input your numbers.