How many ml of 20 percent acid should be added to pure acid to make 70 ml of 30 percent acid?

61.25%

Step-by-step explanation:

How many ml of 20 percent acid should be added to pure acid

to make 70 ml of 30 percent acid?

:

let x = amt of 20% mixture

then

(70-x) = amt of pure acid

:

0.20x + (70-x) =0 .30(70)

0.20x + 70 - x = 21

= 21 - 70

-0.8x =-49

x = 61.25%

x = +61.25 ml of 20% stuff

mr. flanders’ class sold 47 doughnuts and   mr. rodriquez’s class sold 38 cartons of milk

step-by-step explanation:

let x be the number of doughnuts sold by mr. flanders’ class and y be the number of cartons sold by mr. rodriquez’s class.

1. together, the classes sold 85 items, then

x+y=85.

2. both classes earn earned $104.49 for their school. if doughnuts were sold for $1.35 each, then x doughnuts costed $1.35x. if cartons of milk were sold for $1.08 each, then y cartons costed $1.08y. hence,

1.35x+1.08y=104.49.

3. solve the system of two equations: