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there are three sources of resistance in a parallel ciruit. Two of them are rated at 20ohms, the other at ohms. What is the curuit's total resistance? A)20 ohms B)12 ohms C)8 ohms D)5 ohms

letter B

You haven't stated the third resistance, but both A) and B) are not possible for any value in parallel with two 20 ohm resistors. The only possible answers are C) and D).

using 1/R(total) = 1/R +1/R +1/R

1/20 +1/20 =0.1

if the unstated value =x

A)

so 0.1 +1/x = 1/20 = 0.05
which requires a -ve value for x

B)

so 0.1 + 1/x = 1/12 = 0.0833
which requires a -ve value for x

C)

so 0.1 + 1/x = 1/8 = 0.125
which requires a value for x=40 ohms

D)

so 0.1 + 1/x = 1/5 = 0.2
which requires a value for x=10 ohms

To find the total resistance of a parallel circuit, you need to use the formula:

1/RTotal = 1/R1 + 1/R2 + 1/R3 + ...

In this case, there are three sources of resistance. Two of them have a rating of 20 ohms each, and the other does not have a rating mentioned. Let's assume the resistance of the third source is "R3" ohms.

Plugging in the known values into the formula:

1/RTotal = 1/20 + 1/20 + 1/R3

To add fractions with different denominators, you need to find a common denominator. In this case, the common denominator is 20R3. Let's multiply each term by 20R3 to find the common denominator:

20R3/RTotal = (20R3/20) + (20R3/20) + (20R3/R3)

Simplifying:

20R3/RTotal = R3 + R3 + 20

Now we can combine like terms:

20R3/RTotal = 2R3 + 20

To solve for RTotal, we need to isolate it on one side of the equation. Let's cross-multiply:

20R3 = (2R3 + 20) * RTotal

Expanding the right side:

20R3 = 2R3 * RTotal + 20 * RTotal

Subtracting 2R3 * RTotal from both sides:

20R3 - 2R3 * RTotal = 20 * RTotal

Factoring out RTotal:

20R3 = RTotal (20 - 2R3)

Now we have an equation with RTotal on one side. To find the value of RTotal, we need to divide both sides by (20 - 2R3):

RTotal = 20R3 / (20 - 2R3)

However, since we don't have the value of R3, we cannot determine a precise value for RTotal. Therefore, the correct answer is E) Cannot be determined from the given information.