Can you solve this quiz question that’s been driving people crazy for generations?
On TikTok, radio presenter Rob Gormley posed the pub quiz question he “still uses to this day to annoy people”. He first heard the question “some years ago”, when it apparently “caused a war” in a boozer.
While people insisted they had the right answer, they were actually totally wrong. Take a look below and see if you can get it correct…
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?”
Sounds simple, right? Think very carefully about how many times the number 7 appears in the numbers 1 to 100 and note down your answer.
Answer
If you wrote down the number 20, then you’d be correct. But there are few parts of the solution that end up tripping people up.
When you count the numbers, it’s easy to just jump to all of the ones ending in seven – 17, 27, 37, etc. If you remember that 77 needs two sevens, then this method brings you to 11, which is what many people in the comments answered.
But there’s a key component missing – all the numbers starting with seven. There are 10 numbers that start with a seven, 70 through to 79. Some people answered 19 as the total, but they also forgot the second seven in 77. So, with all the numbers starting and ending in seven accounted for, the answer is 20.
The TikTok video has garnered 14,400 likes since it was posted by Rob – and many admitted it had left them scratching their heads.
One replied: “I was SO SMUG that I counted both the sevens in 77 before I realised (too late) my answer was still mega wrong.”
Another said: “Failed. Started with 10, then realised the 70s.” And a third added: “I thought 19 but it’s 20 because 77 has two 7s.”