Answer:
4 ounces
Explanation:
I'm assuming when it says:
% it means 33.3333333333 instead of 33/3.
Anyways under that assumption, we currently have 20 ounces in the grape juice, since 4 ounces is grape juice concentrate and 16 ounces is water. So currently let's just say that the total amount of grape juice concentrate is going to be:
where x is the amount of grape juice concentrate you need to add to make it 33.33%. The next thing to know is how to calculate how much percent a is of b. This can be calculated using the equation:
. So in this case the a is going to be the grape juice concentrate, and the b is going to be the entire mixture (water and grape juice). Since the concentrate is having x added to it, that means the entire thing is also having x added to it. This means we have the equation:
, since we already have 4 ounces of grape juice concentrate, and we already have 20 ounces in total (16 ounces of water + 4 ounces of grape juice). This is going to be equal to 33.33%, or in other words 33 1/3. So to make this a bit easier, I'm going to convert this mixed fraction into one fraction, this gives you the fraction:
. So now that's all left to do is set these two expressions equal to each other and solve for x
Original equation
Divide both sides by 100
Keep fraction, change division to multiplication, flip 100
The 100 in the numerator will cancel out the one in the denominator
Multiply both sides by 20+x
Multiply both sides by 3
Distribute the 3
Subtract x from both sides
Subtract 12 from both sides
Divide both sides by 2
So Kahn needs to pour 4 more ounces of grape juice, to double check this, since the mixture already has 4 ounces of grape juice, this means the final mixture will have a total of 8 ounces of grape juice concentrate, and a total of 24 ounces, since it already had 16 ounces of water, and 4 ounces of grape juice and now there is 4 more ounces of grape juice being added, so a total of 24 ounces. this means that 8/24 will be grape juice concentrate or in other words:
and when you multiply this by 100 (to convert to percent), you get 100/3 or 33 1/3%