This book is designed as an advanced guide for mathematical methods in the science. It covers many topics of practical Statistics: Descriptive Statistics applied in the science: frequency tables for ungrouped and grouped data, position statisticians: arithmetic mean, median, mode, quartile and decile, dispersion statisticians: variance, standard deviation, variation coefficient and average deviation, statistician tables and resume, histograms and frequency polygons, Chebishev Theorem and Slant; Inferential Statistics: combinations, permutations and variations, classical probability, probability distribution for discrete and continuous random variable, joint probability distribution, expectation value, variance and covariance, discrete distributions: uniform, binomial, multinomial, poisson, geometric, hypergeometric and the binomial negative distribution, continuous uniform distribution: uniform, exponential, gamma, chi-square, normal logarithmic, weibull, normal, data collection (sampling), central limit theorem, estimation and confidence intervals for a mean (s known and s unknown) and for a proportion, selection of the right size of a sample, hypothesis testing of a sample, significance tests of one and two tails, tests for the population mean (s known and s unknown), the p value for the hypothesis testing, test related with proportions, hypothesis testing for two samples for independent samples and dependent samples, test of proportion of two samples, t joint test, analysis of the variance, F distribution, comparison of two variances of populations, Anova test, inferences about pairs of means, Anova two way, the method of the least square method for a polynomial fit (regression analysis), correlation coefficient, application problems etc. It is included the deduction of many formulas in order to clear the concepts of Statistics applied in science . It is hoped that this book fills all needs of the students to get the fundaments of the Statistics and to achieve the interest and motivation of the students for this topic.