i. X on Y => X = a + by
ii. Y on X => Y = a + bx

There are two methods of calculating Standard deviation in an individual series.
a) Deviations taken from Actual mean
b) Deviation taken from Assumed mean

1. It is defined as the positive square-root of the arithmetic mean of the square of the deviations of the given observation from their arithmetic mean.
2. The standard deviation of the population is denoted by the Greek letter σ (sigma) The standard deviation of sample is denoted as 's'.

The degree of variation is evaluated by various measures of dispersion. There are two kinds of measures of dispersion, namely
1. Absolute measure of dispersion
2. Relative measure of dispersion

1. In Medical sciences, statistical tools are widely used.
2. In order to test the efficiency of a new drug or to compare the efficiency of two drugs or two medicines, t - test for the two samples is used.
3. More and more applications of statistics are at present used in clinical investigation.

(i) Based on characteristics there are quantitative and qualitative data.
(ii) Qualitative data is classified as nominal data and rank data.
(iii) Based on the data sources there are primary data and secondary data.

The branch of statistics concerned with using sample data to make an inference about a population of data is called Inferential Statistics.

There are two major types of statistics.
(i) Descriptive statistics
(ii) Inferential statistics

\(\bar { X } =A+\frac { \sum { d } }{ n } \)
\(=68+\frac { 31 }{ 5 } \)
= 68 + 6.2 = 74.2
Ans: 74.2