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please help fr , like i acc need help

Please Help Fr Like I Acc Need Help class=

Sagot :

reinhard10158

Step-by-step explanation:

first a little help, how they got the equations :

in total they need 15 liters.

so, whatever x and y are, but together they must be 15 L.

x + y = 15

then, we are mixing x liters of 20% alcohol with y liters of 100% alcohol, that have to result in a 40% solution of (x+y) liters :

0.2x + y = 0.4(x+y)

we know from the first equation that x+y = 15, so the second equation is actually

0.2x + y = 0.4 × 15 = 6

so, we have

x + y = 15

0.2x + y = 6

do you notice something ? there is a "+ y" in both equations.

so we can actually subtract the second equation from the first, eliminate y and solve for the remaining x. and then use one of the original equating to get also y :

x + y = 15

- 0.2x + y = 6

---------------------

0.8x 0 = 9

0.8x = 9

x = 9/0.8 = 11.25 liters

x + y = 15

11.25 + y = 15

y = 15 - 11.25 = 3.75 liters

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