SOLUTION: My child has a maths question in Foundation of Mathematics by A J Sadler and the answer in the book = 50. I do not get that answer but my child can using calculator equations. My c

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Question 69687: My child has a maths question in Foundation of Mathematics by A J Sadler and the answer in the book = 50. I do not get that answer but my child can using calculator equations. My child needs to understand the method and I do not know where I'm going wrong. I can normally work these problem out but I need help with this one:
1/R = 1/R1 + 1/R2 + 1/R3 where R = 20, R2 = 40 and R3 = 200
1/20 = 1/R1 + 1/40 + 1/200

Found 2 solutions by stanbon, funmath:
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
1/R = 1/R1 + 1/R2 + 1/R3 where R = 20, R2 = 40 and R3 = 200
1/20 = 1/R1 + 1/40 + 1/200
Then:
1/R1 = 1/20-1/40-1/200
1/R1 = [10 - 5 -1]/200
1/R1 = 4/200
1/R1 = 1/50
R1 = 50
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Cheers,
Stan H.

Answer by funmath(2933) (Show Source):
You can put this solution on YOUR website!
My child has a maths question in Foundation of Mathematics by A J Sadler and the answer in the book = 50. I do not get that answer but my child can using calculator equations. My child needs to understand the method and I do not know where I'm going wrong. I can normally work these problem out but I need help with this one:
1/R = 1/R1 + 1/R2 + 1/R3 where R = 20, R2 = 40 and R3 = 200
1/20 = 1/R1 + 1/40 + 1/200
The LCD is 200R1, multiply everything by 200 to clear the fractions.

Happy Calculating!!!!