How much gram of sorbitol, should I to weigh on the balance?

[Cyrus the great]

Homework Statement

I have 4.6 gram of starch and I want to add 30 % of sorbitol to xylan. How much gram of sorbitol, should I weigh on the balance?

Homework Equations

The Attempt at a Solution

 

[Dr. Courtney]

It is not clear whether you are talking about xylan as your starch, or whether it is in addition to the starch and sorbitol.

It is also unclear whether you want to add 30% of the existing amount or whether you want sorbitol to be 30% of the total amount.

 

[Cyrus the great]

yes I meant xylan as my starch and I want sorbitol to be 30% of the total amount.

 

[Dr. Courtney]

Let x be the amount of sorbitol to add, in grams.

Let T be total amount.

x = 0.3*T

But you can also express the total amount T in terms of x and the initial amount of starch.

Do that, substitute into the above equation, solve for x.

Double check that x is 30% of T.

 

[Cyrus the great]

I want to add 30 % sorbitol to my starch. Therefore, I calculated like below.
starch starch
70 100
4.6 X

X=4.6*100/70= 6.50 g. So, amount of sorbitol needed is 6.5-4.6=1.96 g

But If I do like your way X=4.6 * 0.3=1.38 gram

Now I have got confused. Which number is correct?

 

[Cyrus the great]

I want sorbitol to be 30% of the total amount. So if I have 70 % starch I have 4.6 g and if I want to have 100 % then how much starch it would be which becomes 6.5.

X=4.6*100/70= 6.57

Then I deducted 6.5 from 4.6 which it becomes 6.5-4.6=1.97 gram of sorbitol should be added to the starch.

Is my calculation correct?