# Thread: normal distribution

1. ## normal distribution

A batch of 5% tolerance resistors of nominal value 1000 ohms, has a mean

value of 1000 and a standard deviation of 50. The distribution of

values is normal and a table of the normal distribution is attached.

(i)Four resistors are taken at random and added together.

Calculate the probability that the resistance of the series
combined is within the range 3950 to 4050.

Help on this would be very much appreciated.

Thanks

2. Originally Posted by pip1690
A batch of 5% tolerance resistors of nominal value 1000 ohms, has a mean

value of 1000 and a standard deviation of 50. The distribution of

values is normal and a table of the normal distribution is attached.

(i)Four resistors are taken at random and added together.

Calculate the probability that the resistance of the series

combined is within the range 3950 to 4050.

Help on this would be very much appreciated.

Thanks
The distribution of the sum of $\displaystyle n$ resistor values has mean $\displaystyle n \times \mu$ and standard deviation $\displaystyle \sigma/ \sqrt{n}$ and has a normal distribution.

In this case $\displaystyle n=4,\ \mu=1000,\ \sigma=50$.

RonL