Arithmetic error when computing the student hours

[dcoraboeuf]

The stack trace shows like:

Non-terminating decimal expansion; no exact representable decimal result. [net.iteach.web.support.DefaultErrorHandler]
java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.
    at java.math.BigDecimal.divide(Unknown Source)
    at net.iteach.service.impl.AbstractServiceImpl.getHours(AbstractServiceImpl.java:63)

The divide operation must be bounded.