1) A 40% saline solution is to be mixed with 60% saline solution to obtain 8 liters of a 55% saline solution..

/
8l of 55% has 4.4 l of saline
0.4x+0.6y=4.4
x+y=8
solvex=2,y=6
2 l of 40%
6l of 60%

okay, i learned a bucket method that will help you solve mixture problems. draw a box in a top left, one in the top right, and one below in the center (sort of like eyes and a mouth.  inside the top left your gonna write your percent of your first item (i.e 40%, or 4% in problems 1 and 2 respectively) the top right box gets the percent of the second mixed item. (i.e. 60% or 6%). the bottom box gets the goal percent on the inside (i.e. 55% or uh..too lazy to figure it out w/o calculator but just figure out what percent 1740 is of 4000. ) below each box your gonna write the amount of each solution (prob. 1 you would take 8 liters and put it at the bottom, thats your goal amount. box 1 would be x and box 2 would be 8-x, the goal product minus whatever amount you put in in the first place...) (prob. 2 would be 4000-x and x and the bottom is the return of 1740). then for each problem you take the percents and convert to decimels. now, the top left box, take the inside and multiply it by the outside, do the same to the second box. add these together and set them equal to the product of the third box (outside times inside) and then your done...sorry easy to explain with pictures...hope i could help...d*** three probs huh? sorry, lets see...okay if nickels are x, then quarters are 2x + 9 (basic math word prob...) if nickels are worth 5 cents, then in a percent of a dollar you have .05, multiply that by x. ill refer to this as your nickel product. next, if quarters are 25 cents, that = .25 as a percent of a dollar. (dollar = 1 or 100%). multiply that by your amount of quarters (2x+9). this is quarter product.  now simply add nickel product and quarter product and set them equal to your final amount, 5.35