Hannah’s Sweets is the latest viral math problem stumping the Internet

Nearly two months after people were stumped trying to figure out when Cheryl’s birthday was, there’s a new math problem that’s making brains hurt.

It has to do with a woman named Hannah and her sweets.

The question was from the Edexcel exam, a mathematics exam administered in the United Kingdom generally given to teenagers.

Here it is. Watch out, it escalates quickly.

There are n sweets in a bag. 6 of the sweets are orange. The rest of the sweets are yellow.

Hannah takes a random sweet from the bag. She eats the sweet.

Hannah then takes at random another sweet from the bag. She eats the sweet.

The probability that Hannah eats two orange sweets is 1/3.

Show that n² – n – 90 = 0.

The question seems a just a smidge harder than Cheryl’s birthday, which was rooted in logic rather than probability.  And it caused British students to vent their frustration on Twitter, causing #Edexcelmath and #Hannahssweets to trend.

So how do you answer it? Here’s what smart people said online.

Or…

According to The Guardian, there is a 6/n chance the first sweet Hannah takes from the bag will be orange. There are six orange sweets and n sweets.

If Hannah takes another sweet, there is a 5/(n-1) chance her second selection will also be orange. One is subtracted from each number because there is one less sweet than Hannah originally had.

So the chance of getting two orange sweets in a row is the 6/n multiplied by 5/(n-1).

Now we have 6/n x 5/n-1.

We already know the chance of Hannah getting two orange sweets is 1/3 so now the equation becomes 6/n x 5/n-1 = 1/3 (the probability worked out first is equal to the 1/3).

Now it’s a matter of rearranging and expanding the equation.

(6×5)/n(n-1) = 30/(n² – n) = 1/3

90/(n² – n) = 1

(n² – n) = 90

Answer:  n² – n – 90 = 0