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# chemistry thingy with pennies

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I have a chem lab and we need to find the amount of two different weight pennies in a film canister of 15 pennies just by the weight.

Do i just set up to equations like this:

3.1x+2.51y=43.97

x+y=15

??

Sep 13, 2017

#1
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3.1x + 2.51y  =  43.97

x + y  =  15

I don't know if these are the two correct equations; but, if they are, one way to solve them is by solving the second equation for x and then substituting that value in the first equation:

x + y  =  15     --->     x  =  15 - y

3.1x + 2.51y  =  43.97     --->     3.1(15 - y) + 2.51y  =  43.97

46.5 - 3.1y + 2.51y  =  43.97

46.5 - 0.59y  =  43.97

-0.59y  =  -2.53

y  =  4.29

Substituting that value into the equation  x = 15 - y     --->     x  =  15 - 4.29      --->     x  =  10.71

Sep 13, 2017

#1
+1

3.1x + 2.51y  =  43.97

x + y  =  15

I don't know if these are the two correct equations; but, if they are, one way to solve them is by solving the second equation for x and then substituting that value in the first equation:

x + y  =  15     --->     x  =  15 - y

3.1x + 2.51y  =  43.97     --->     3.1(15 - y) + 2.51y  =  43.97

46.5 - 3.1y + 2.51y  =  43.97

46.5 - 0.59y  =  43.97

-0.59y  =  -2.53

y  =  4.29

Substituting that value into the equation  x = 15 - y     --->     x  =  15 - 4.29      --->     x  =  10.71

geno3141 Sep 13, 2017