# The most difficult math riddles

A list of math related questions that are most often answered incorrectly

Mathematics quiz
## Augustus was born on 1 January 10BC. Which birthday did he celebrate at 1 January 10AD?

19. There was no year number zero. There were only 1999 years between 1000BC and 1000AD.

very hard

39%

19

19

39%

20

20

35%

21

21

19%

80

80

5%

Created by: Gizem İsmailoğlu.
Statistics based on 12969 answers in 4 languages
»

## Typically, how many leap years are in a century?

24. The Gregorian Calendar omits 3 leap days every 400 years, omitting February 29 in the 3 century years (integer multiples of 100) that are not also integer multiples of 400. For example, 1600 was a leap year, but 1700, 1800 and 1900 were not. Similarly, 2000 was a leap year, but 2100, 2200, and 2300 will not be.

hard

44%

20

20

9%

24

24

44%

25

25

42%

100

100

4%

Created by: ex-terminator.
Statistics based on 10845 answers in 2 languages
»

## If Earth's radius was larger by 1 meter, how much longer would its equator be?

By approx 6 meters. For each circle, the length of the circumference is c=2πr. Hence, if a radius grows by 1 meter, the circumference grows by 2 π meters - no matter what the initial value of radius was.

hard

46%

by approx 6 meters

by approx 6 meters

46%

by approx 6 kilometers

by approx 6 kilometers

16%

by approx 60 kilometers

by approx 60 kilometers

20%

by approx 6000 kilometers

by approx 6000 kilometers

16%

Created by: SpikeMe.
Statistics based on 16816 answers in 2 languages
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## Which famous scientist was born on the Pi day? (March 14)

Albert Einstein. 14 of March is celebrated on many schools and universities as both Pi Day and the birthday of Albert Einstein. On of the traditions is the 'Pi Pie' (pictured).

hard

48%

Albert Einstein

Albert Einstein

48%

Blaise Pascal

Blaise Pascal

17%

Isaac Newton

Isaac Newton

16%

all of the above

all of the above

17%

Created by: globalquiz.org.
Statistics based on 9448 answers in 4 languages
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## How many possible code combinations are there for this kind of lock?

10000. The possible codes are from 0000 to 9999 inclusive. There are 10 possibilities for each ring, thus there are 10*10*10*10 possible codes.

hard

51%

999

999

4%

1000

1000

6%

9999

9999

36%

10000

10000

51%

Created by: Teddy.
Statistics based on 10034 answers in 2 languages
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## Which of the following is a prime number?

16769023. A prime number has no positive divisors other than 1 and itself. Hence, a prime bigger than 2 cannot be even. All prime numbers bigger than 5, written in the usual decimal system, end in 1, 3, 7, or 9.

average

66%

23882990

23882990

9%

16769023

16769023

66%

38377296

38377296

8%

11723835

11723835

15%

Created by: Sumit Tamang.
Statistics based on 12211 answers in 2 languages
»

## Let's say the stock price was 10 two days ago. It has dropped by 50% yesterday and raised by 50% today. What is the stock price now?

7.5. Stock price was 10 two days ago. Yesterday it dropped by 50% to 5. Today it raised by 50% (of 5) to 7.5

easy

72%

10

10

14%

12.5

12.5

11%

7.5

7.5

72%

20

20

2%

Created by: globalquiz.org.
Statistics based on 8617 answers in 2 languages
»

## How many edges does a Möbius strip have?

One. The Möbius strip is a surface with only one side and only one boundary component (edge). A line drawn starting from the seam down the middle will meet back at the seam but at the "other side". If continued the line will meet the starting point and will be double the length of the original strip.

easy

73%

one

one

73%

two

two

18%

three

three

4%

four

four

3%

Created by: globalquiz.org.
Statistics based on 12221 answers in 4 languages
»

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