# Probability » Conditional probabilities and (in)dependence

If a table is given and a probability is asked, watch out, as may be you have a conditional probability.

With a conditional probability, the total number of possibilities is not the total number of outcomes. Instead you have a subgroup.

*Example*

Boys | Girls | Total | |

Left-handed | 3 | 4 | 7 |

Right-handed | 8 | 11 | 19 |

Total | 11 | 15 | 26 |

*Question 1*

Calculate the possibility of a person being left-handed.

Answer:

The number of good outcomes is 7.

The total number of possible outcomes is 26.

The probability is therefore 726

*Question 2*

Calculate the probability a girl is a right-handed person.

Answer:

The number of good outcomes is 11.

The total number of possible outcomes is 15.

The probability is therefore 1115

*Question 3*

Calculate the possibility a right-handed person is a girl.

Answer:

The number of good outcomes is 11.

The total number of outcomes is 19.

The probability is therefore 1119

*As you can see, it is important to read the question carefully.*