Question

A laboratory technician has made up a stock mixture of two chemicals, X and Y, ready for use
by all of the groups in Year 9 at a High School. He has mixed 6.0 kg which is 4
1 of X and 4
3 of
Y. He realizes that he has used the wrong mix and, rather than waste the chemicals he has used so far, he is going to add some more of chemical X so that the mix consists of 40% of X
and 60% of Y.
What mass of chemical X must he add?

Hi, I have no idea how to solve this. Thank you in advance.

Answer 1

Horrible text formatting. I have no idea what "4
1 of X and 4
3 of
Y" means
So, for the sake of argument, I'll go with 1/4 X and 3/4 Y.
Consider just the amount of X and follow it through the situation.
He started with 1/4 * 6 = 1/5 kg of X in 6 kg of mix
Now he wants to add z kg of 100% X so that he winds up with 40% of 6+z kg of mix
1.5 + z = 0.40 (6+z)
z = 1.5

You don't have to worry about tracking the Y. It will take care of itself.
So, let's check to see that our answer is right.
1.5 + 1.5 = 3 = .40 * (6+1.5)
yep