<PRE><B>Question 157183</B>
 A group of ten 6 and 12 volt batteries are wired in series; the sum of their voltages is 84 volts. How many of each type of battery are used? 
6x + 12x = 84
18x = 84 does not work
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Call the 12V batteries T and the 6V S
There is a total of 10 batteries, so 
T+S=10
12T + 6S = 84
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T=10-S
Sub for T
12(10-S) + 6S = 84
120-12S + 6S = 84
120 -6S = 84
-6S = -36
S = 6
T = 4

Check:
6*6 + 12*4 does = 84


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