Imagine an HIV test that is 95% accurate (false positive rate of 5%) and around 2% of the tested population is infected with HIV. What is the probability that you actually have HIV when your test comes back positive?

On a regular 12-hour digital clock how many times would the same three digits in a row be displayed (e.g. 1:11, 11:12, 12:22) in one day?

Two days ago Lilly was 7 years old. Next year she will turn 10. How can this be?

There are many English words that you can add an “s” to make it plural. But far fewer words become singular when you add an “s”. What are two examples of these much rarer words?

How many country names can you find in the following statements?

Don’t reach in a crack in the rocks, there might be snakes in there.
While I was on the highway called the Alcan, a daily occurrence was car breakdowns.
The top social class, as defined by many, is the upper-upper.

Toby likes indigo but not red. He likes onions but not turnips. He likes forms but not shapes.

According to the same rule, does he like tomatoes or avocados?