Tough pub quiz question is leaving people puzzled – can you solve it?

The pub quiz question caused arguments many years ago (stock photo) (Image: Getty)

This mind-boggling quiz question will certainly test your mental agility.

Pub quizzes are a great source of entertainment, regardless of the depth of your general knowledge. You might be the type who effortlessly answers every question correctly, or perhaps you're just there for a good laugh with your friends, even if you don't get a single answer right.

The questions posed in a pub quiz usually span various categories such as sports, films, and history. However, they can also throw in some riddles or brainteasers that require you to think outside the box to find the answer.

One such question is said to have "caused war" at a pub quiz many years ago - even though it has a very straightforward answer.

In a TikTok video, radio presenter Rob Gormley shared the pub quiz question he "still uses to this day to annoy people", and asked his viewers if they could solve it.

He first heard the question "some years ago" when it sparked "ructions" as participants were convinced they had the correct answer - despite many of them being wrong.

The question was: "A builder builds 100 houses. The last thing the builder has to do is put numbers on the doors. They're numbered 1 to 100 - it's not a trick question. 100 houses, he needs numbers from 1 to 100.

"How many number 7s is the builder going to need?"

It may seem straightforward, but many people fall into the same trap when answering the question. Consider carefully how many times the number 7 appears in the numbers 1 to 100, and when you think you've got the answer, scroll down to see the solution.

Answer

The correct answer is indeed 20, but many individuals make a common error in their calculation. When counting, it's easy to focus solely on numbers ending in seven, such as 17, 27, and 37.

However, using this method would only yield 11 sevens, which is the incorrect answer given by several people in the comments. The mistake lies in overlooking the numbers that start with seven, specifically 70 to 79, which adds 10 more sevens.

Some people arrived at 19, but they failed to account for the second seven in 77. By including all numbers starting and ending with seven, the correct answer is 20.

As one commenter pointed out: "20. Worked it out before you finished speaking. Very simple logic and worrying that people argued about it."

Another commenter added: "I was SO SMUG that I counted both the sevens in 77 before I realised (too late) my answer was still mega wrong."