We start with nine raffle tickets. Bob puts one more in right before the drawing, so now we have ten raffle tickets in total, two of which belong to Bob.

Since 2 out of 10 tickets will make Bob win, he has a 20% chance of winning.

We can find the chance by setting up a fraction of ripe strawberries out of total strawberries. We know that there are 20 strawberries in total, and that 4 of them are ripe.

We can reduce the fraction be removing a common factor.

Finally, we need to convert our fraction to a percentage.

There is a 20% chance that Bob will pick a ripe strawberry.

This question deals with a probability "or" statement. When a question asks about two different outcomes in the context of "or," you must add the probability of the two outcomes together.

If three of Marta's books are fiction and three are non-fiction, then we know that half of her books are fiction and half are non-fiction.

To find the chance of picking a fiction OR non-fiction book, we will need to add the two probabilities together.

There is a 100% chance that the book she picks will be fiction or non-fiction.

Let's start by looking at how many names are left in the bag.

Before Mary's name was picked by the teacher, there were 11 names. However, since Mary's name has been removed, there are only 10 names left in the bag.

The chance that Mary picks Rebecca's name will be equal to:

Rebecca's name only appears once out of ten total names:

The chance that Mary picks Rebecca will be equal to one-tenth, or 10%.

Initially we have 5 packets of how chocolate, 2 of which have marshmallows. We can diagram this, with C representing regular hot chocolate and M representing hot chocolate with marshmallows:

C C C M M

Jeff picks a packet without marshmallows, leaving:

C C M M

If Charlie picks at random, there are 4 packets left and two of them have marshmallows. His chance of getting marshmallows is:

We can reduce the fraction to find our final answer.

Whether a coin lands on heads or tails the first time it is flipped does not affect how it will land in a future flip. Each flip is an independent event.

When a coin is flipped, there is a 50% chance it will be heads and a 50% chance that it will be tails. Since the first flip has no effect on these odds, the chance Mary's second coin flip will be heads is still equal to 50%.

Given that 25% of the oranges at a grocery store are underripe, and that 25% of 8 is 2, the odds indicate that 2 oranges should be underripe. Therefore, 2 is the correct answer. 

If there are 5 shirts in a store and 1 has a rip in it, there is a  chance of buying the shirt with the rip. 

If there are 5 ties, one of which also has a rip, then the probability of buying the tie with a rip is also . 

Therefore, the probability of buying both ripped articles of clothing is .

Given that , the correct answer is "black" because there are  black marbles.

If Bob rolls a pair of dice, the potential numbers that he could roll are below:

Thus, there are 11 possible numbers that he could roll, of which 5 are prime:.

Therefore, the probability of rolling a prime number is .