Verified answer

20 ml of 10% vinegar solution will contain

=20*10/100 ml

=2 ml of vinegar

Let x ml of vinegar be added to the solution.

Total vinegar = 2ml + x ml = x+2 ml

Total volume = 20ml + xml = x+ 20 ml

To make it 25% solution

(x+2)/(x+20)=25/100

100(x+2)=25(x+20)

100x+200=25x+500

75x=300

x=4

Ans. 4 ml of vinegar must be added.

2/5=x/x+20

Cross multiply: 2(x+20)=5x

2x+40=5x

40=3x

x=40/3 or 13.333333333

so about 33 and 1/3 ml.

AH NEVER MIND! i got 2 more days of school and 1 more day of math and i'm answering a question that i'm not completely sure i know. good luck though. =P