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March 1, 2015

March 1, 2015

Posted by **Melinda** on Tuesday, January 10, 2012 at 7:16pm.

1.Two resistors a and b are connected in parallel. The total resistance R in such a circuit is found by formula R= 1/a + 1/b. If R=5/6 ohms and b is one more ohm than a, find the number of ohms in a and b.

2. The profit function for producing blank CD's was projected to be P(x)=x^2 + 5x-6 where x is the number of CD's produced in hundreds. The average profit for a cd is found by P(x)/x. At what level of production must the company produce the CD's for the average profit to be greater than zero?

- Math -
**Reiny**, Tuesday, January 10, 2012 at 7:32pm1. aren't you told that

b is one more ohm than a ?

so -----> b = a+1

sub in the equation

5/6 = 1/a + 1/(a+1)

multiply by 6a(a+1) , the LCD

5a(a+1) = 6(a+1) + 6a

5a^2 + 5a = 6a + 6 + 6a

5a^2 - 7a - 6 = 0

(a-2)(5a + 3) = 0

a = 2 or a = -3/5, but I believe that a > 0

so a = 2 ohms and b = 3 ohms

check:

1/2 + 1/3 = 5/6 , all is good!

- Math -
**Damon**, Tuesday, January 10, 2012 at 7:33pm5/6 = 1/a + 1/(a+1)

5 a(a+1) = 6(a+1) + 6 a

5 a^2 + 5 a = 6 a + 6 + 6 a

5 a^2 - 7a - 6 = 0

(5a+3)(a-2) = 0

a = 2

b = 3

- Math -
**Damon**, Tuesday, January 10, 2012 at 7:39pmWhere is P(x) zero?

(x+6)(x-1) = 0

You can not make a negative number of blank CDs

so where x>1 the profit is positive, so is P(x)/x

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