If an averaging amplifier has 4 inputs, the ratio Rf/Ri must be:a.4b.0.2c.25d.0.25

To determine the ratio Rf/Ri for an averaging amplifier with 4 inputs, we need to consider the formula for the gain of an averaging amplifier. The gain (Av) of an averaging amplifier is given by the equation:

Av = -Rf/Ri

where Rf is the feedback resistor and Ri is the input resistor.

In this case, we have 4 inputs, so the gain equation becomes:

Av = -4Rf/Ri

To find the ratio Rf/Ri, we can rearrange the equation:

Rf/Ri = -Av/4

Now, we need to determine the value of Av. Since the question does not provide any information about the gain, we cannot determine the exact value. Therefore, we cannot determine the ratio Rf/Ri.

Hence, the correct answer is not provided in the options given (a. 4, b. 0.2, c. 25, d. 0.25).