Investment bankers work with mergers and acquisitions, trading, and engage in research analysis. At the end of the day their job is to make money, and this requires studying figures, indicators and making smart predictions. Taking calculus is a vital math class no investment banker should miss because it is a branch of mathematics that helps people make predictions. Boston College's course in calculus includes the study of logarithmic functions. The logarithm of a number is the exponent to which the fixed-value base must be raised to produce a desired number. Such skills help investment bankers make financial predictions.
Statistics deals with probability distributions, hypothesis testing, estimations and many other topics that directly relate to the roles of bankers. Often people in the banking industry will have B.S. degrees in finance, and statistics is a core course in most finance curricula, especially for those who work in central banks. The European Central Bank describes statistics as "relevant to all functions and tasks of the central bank" and that it enables proficiency in various areas that include "financial stability and banking supervision [and] payment systems."
Some people will fill entry level positions in big banks with the intention to go to grad school after they have some work experience. Anyone taking an entry level job in banking probably wouldn't need to know any math more advanced than precalculus. Precalculus teaches a basic introduction to problem solving with equations, polynomials, functions, exponential functions, logarithmic functions, trigonometric functions, trigonometric identities and equations, systems of equations and inequalities, mathematical induction, the binomial theorem and several other mathematical areas. Precalculus is also the class where most students learn how to use a graphing calculator for the first time. Precalculus is offered in high school as an AP class but is also commonly found in college curricula.
If you work your way through college as a teller at Wells Fargo or Bank of America you don't need to have the advanced math skills that the big players on Wall Street have. Algebra is commonly offered in high schools and community colleges but can also be found nestled in between the lines of a four-year college curriculum. Most algebra classes teach percentages, fractions, linear and quadratic equations, inequalities, graphs and other topics. A bank teller primarily counts money, reconciles cash drawers and sells financial products to consumers. Some of these products require a teller to have algebra knowledge simply so he can demonstrate how the products work financially. For example, algebra will help tellers demonstrate savings accounts,certificates of deposit, mutual funds and securities.