Question

Please help me study I have to take a test in two hours, & nobody will help out.

Show an equation and a solution for the problem. Arnold needs a 25% solution of nitric acid. He has 20 milliliters (ml) of a 30% solution. How many ml of a 15% solution should he add to obtain the required 25% solution?

Answer 1

well if you have a test we better get busy

Answer 2

you there?

Answer 3

i will walk you through it if you like.

Answer 4

I don't get it.
& I need help.

Answer 5

ok we can do it

Answer 6

first off we need to find something, namely the number of ml of 15% solution to add, so we call it X so we can solve for it ok?

Answer 7

you have 20 ml of a 30% solution. to this you are going to add X ml of 15% solution, so the total amount of solution will be 20 + X. the 20 you started with and the X that you added

Answer 8

when you get done, you want 25% of the total to be acid, and 25% of 20 + X is written as .25(20+X)

Answer 9

that will be on one side of the equal sign.

Answer 10

now we have 20 ml if 30% solution and 30% of 20 is .30 * 20 = 6

Answer 11

to this we are going to add X of the 15% solution and 15% of X is .15X. so the total amount of acid we will have will be
6 + .15X

Answer 12

the 6 ml of acid plus the 15% of the X that we add. that will be on the other side of the equal sign. so the equation to solve is
\[6+.15X=.25(20+X)\]

Answer 13

how are we doing so far?

Answer 14

the hard part is setting up the equation. the easier part is solving it. but before we solve it are any steps unclear?

Answer 15

btw i will be happy to write the answer but since you said "i have a test" i am assuming you want to know how to do the problem

Answer 16

Answer would be better.

Answer 17

You asked this question twice. I answered it there.

Answer 18

ok we solve \[6+.15x=.25(20+x)\]
decimals are a pain so multiply everything by 100 to clear them
\[600+15x=25(20+x)\]
\[600+5x=500+25x\]
\[600-500=25x-5x\]
\[100=20x\]
\[x=5\]

Answer 19

notice when i cleared the decimals i had to multiply 6 by 100 as well

Answer 20

@satellite73 Your answer is wrong ... your 15x turned into 5x and you ended up solving the wrong equation. Corret answer is x = 10

Answer 21

@djvu
Can you just write the solution & equation on her.

Answer 22

Look at the image I posted.

Answer 23

The equation to be solved is what satellite73 already posted : 6+.15x=.25(20+x) except he/she made an error in the calculations. Final answer is 10

Answer 24

djvu you are right. somehow my 15x on one line became a 5x on the other. i should really be more careful

Answer 25

Thank you.