Question

to disinfect one quart of stream water to make it drinkable you need to add two tablets of iodine. How many tablets do you need to disinfect 4 quarts

Answer 1

It is already given in the question that 2 iodine tablets are required to disinfect 1 quart of stream water. The thing that needs to be found is the number of tablets required to disinfect 4 quarts. As can be seen in the question, the information's provided are enough to get to the desired answer.
Then
Number of tablets required to disinfect 1 quart of stream water = 2
Number of tablets required to disinfect 4 quart of stream water = 2 * 4
                                                                                                     = 8
So 8 iodine tablets are required to make 4 quart of stream water drinkable.