Question

You want a 50% strength solution of medicine. You have some 20% strength solution and 40 milliliters of a 90% strength solution. How much of the 20% strength solution do you have to add to the 90% solution to get a 50% strength solution?

The answer is 53.3 ml.
I need to know HOW to get THAT answerrrrrr !

Answer 1

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Answer 2

(40*.9+x*.2)/(40+x)=.5

Answer 3

the numerator is the total ml of pure solution, denominator is total milliliters

Answer 4

40 ml *.9 pure/ml + x ml *.2 pure/ml

Answer 5

is that 40.9 or 40 times .9?

Answer 6

40 times .9, x times .2

Answer 7

does the equation make sense?

Answer 8

yeah kind of

Answer 9

no i dont get it ):

Answer 10

ok if you have 40 millilters of 90% HCl solution how much pure HCl do you have?

Answer 11

Idk ): 20% ?

Answer 12

the strength is 90%, so there are .9 ml of HCl per 1 ml of solution. so 40*.9 is the amount of pure HCl. 40*.9=36

Answer 13

HCI ?

Answer 14

oh im just putting a random chemical in it doesnt matter

Answer 15

oh ahaha okay

Answer 16

haha sorry

Answer 17

ok so there are 40*.9 ml from the 90% solution and there are x*.2 ml from the 20% solution where x is however many ml we add

Answer 18

thats the numerator which is the total pure ml

Answer 19

and the denominator is just the total ml of solution, 40+x

Answer 20

pure ml/ total ml = concentration

Answer 21

and the concentration we want is .5 so the whole thing is set equal to .5

Answer 22

okay i get that part !

Answer 23

Do we put anything for X ?

Answer 24

we need to solve for x now, that is the amount we need to add to get .50 concentration solution

Answer 25

so now its just an algebra problem

Answer 26

ohhhhhhhh ok, i gettttttttt it (: Thanksssssssss

Answer 27

you're welcome :)