What is the probability that Susie will grab a black marble after Sally's turn?

To determine the probability that Susie will grab a black marble after Sally's turn, it's important to analyze the scenario involving the total number of marbles and their colors.

The probability of an event is calculated by taking the number of favorable outcomes and dividing it by the total number of possible outcomes. In this case, Susie's chances of selecting a black marble depend on the composition of the remaining marbles after Sally's turn.

If we consider that Sally's selection has not significantly changed the ratio of black marbles to total marbles compared to the initial situation, we can deduce that Susie's probability of grabbing a black marble remains constant. For instance, assume there were originally black marbles in the jar. If the original total number of marbles is 39 and there are 9 black marbles, the probability that Susie grabs a black marble after Sally's turn would indeed be 9 (the favorable outcomes of black marbles) over 39 (the total marbles remaining), which simplifies to 1 in approximately 4.

This alignment of numbers (9 black out of 39 total marbles equating to a simplified ratio of 1 in 4) confirms the reason behind selecting that specific probability for Susie's turn.