Suppose a jar contains 5 red marbles and 23 blue marbles. If you reach in the jar and pull out 2 marbles at random, find the probability that both are red. Write your answer as a reduced fraction.
There are 28 marbles in total in the jar.
To find the probability of pulling out 2 red marbles, we use the concept of probability with replacement.
The probability of pulling out a red marble on the first draw is $\dfrac{5}{28}$.
After removing one red marble, there are 4 remaining red marbles out of 27 total marbles.
The probability of pulling out a red marble on the second draw is $\dfrac{4}{27}$.
To find the probability of both events occurring, we multiply the probabilities:
$\dfrac{5}{28} \times \dfrac{4}{27} = \dfrac{20}{756}$.
This fraction cannot be reduced further.
Therefore, the probability that both marbles drawn are red is $\boxed{\dfrac{20}{756}}$.