2. CHEMISTRY How many liters of 15% acid and 33% acid should be mixed to make 40 liters of 21%
acid solution?
Concentration
of Solution
Amount of
Solution (L)
Amount
of Acid
15%
33%
у
21%
40

Step-by-step explanation:

Concentration            Amount of             Amount

of Solution                   Solution (L)             of Acid

    15%                                x                         0.15x

    33%                               y                         0.33y

    21%                              40                      0.21•40      

x + y = 40    ⇒  x = 40 - y

0.15x + 0.33y = 0.21•40

0.15(40 - y) + 0.33y = 0.21•40

6 - 0.15y + 0.33y = 8.4

  0.18y = 2.4

        y = 13¹/₃

x = 40 -  13¹/₃ = 26²/₃

its 4 because 2 times 2 is 4, if you double the number two you get four