pls help? anyone? >_<
this is embarassing ahhaha

(she's gr 8, i graduated with a science degree lol)

Assume there was x kg of salt and y kg of water initially. It then follows that:

(x + 1)/(x + y + 1) = 1/3 => 3x + 3 = x + y + 1 => -2x + y = 2

So is the resulting solution 30% salt by mass after 1 kg of water is added?

(x + 1)/(x + y + 2) = 3/10 => 10x + 10 = 3x + 3y + 6 => -7x + 3y = 4

x = 2 kg and y = 6 kg

So % salt in original solution = (2 kg)/(2 kg + 6 kg) * 100 = 25%

Answer is C.

say that your initial solution had 'x' kg of salt and 'y' kg of water in it.

when we added 1 kg of salt the solution became 33.3% salt. That is, the mass of salt divided by the mass of salt + water was 1/3

(x + 1) / (x + 1 + y) = 1/3
=> 3(x + 1) = x + 1 + y
=> 2x + 2 = y

then we added 1kg of water

(x + 1) / (x + 1 + y + 1) = 3/10
=> 10x + 10 = 3x + 3y + 6
=> 7x + 4 = 3y

You have two equations and two unknowns now, solve the system. We already have y isolated in the first one, so we can do substitution easily

7x + 4 = 6x + 6
x = 2
=> y = 6

So your initial solution was 2 kg of salt and 6 kg of water -> 25%

edit: I got inb4ed

This post was edited by russian on Jun 9 2016 04:17pm