Question

The blood groups of 200 people are distributed as follows: 50 have type A blood, 65 have B blood type, 70 have O blood type and 15 have type AB blood. If a person from this group is selected at random, what is the probability that this person has O blood type? 

Construct a table of frequencies for the blood groups

Answer 1

$$P(O\ blood\ type)=\dfrac{70}{200}=0.35$$

$$\def\arraystretch{1.5} \begin{array}{c:c:c:c} & Type & Frequency & Relative\ frequency \\ \hline & A & 50 & 0.25 \\ \hdashline & B & 65 & 0.325 \\ & O & 70 & 0.35 \\ & AB & 15 & 0.075 \\ Sum= & & 200 & 1 \\ \end{array}$$