Refer to the IEICE Transactions on Information & Systems (Jan. 2005) study of impedance to leg movement, Exercise 2.46. Recall that Korean engineers attached electrodes  to the ankles and knees of volunteers and measured the voltage readings between pairs of electrodes. These readings were used to determine the signal-to-noise ratio (SNR) of impedance changes such as knee flexes and hip extensions.
a. Six voltage electrodes were attached to key parts of the ankle. How many electrode pairs on the ankle are possible?
b. Ten voltage electrodes were attached to key parts of the knee. How many electrode pairs on the knee are possible?
c. Determine the number of possible electrode pairs, where one electrode is attached to the knee and one is attached to the ankle.

Data from Exercise 2.46

In an experiment to monitor the impedance to leg movement, Korean engineers attached electrodes to the ankles and knees of volunteers. Of interest was the signal-to-noise ratio (SNR) of impedance changes, where the signal is the magnitude of the leg movement and noise is the impedance change resulting from interferences such as knee flexes and hip extensions. For a particular ankle–knee electrode pair, a sample of 10 volunteers had SNR values with a mean of 19.5 and a standard deviation of 4.7. (IEICE Transactions on Information & Systems, Jan. 2005.) Assuming the distribution of SNR values in the population is mound shaped and symmetric, give an interval that contains about 95% of all SNR values in the population.