10 most difficult mathematics riddles A list of ten (out of 23) mathematics related questions that are the most often answered incorrectly Mathematics quiz Which of the following is true for the solution with the pH=0?The OH − ion concentration is smaller than the H+ ion concentration. In chemistry, pH is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. It is the negative of the logarithm to base 10 of the activity of the hydrogen ion .Traditionally the pH is being defined as: pH = - log10 [H+], where [H+] it is a H+ ions concentration in mol/dm^3 (M). So if pH = 0 this H+ ions concentration is 1 mol/dm^3 and the solution is strongly acidic.very hard 24% the OH − ion concentration is smaller than the H+ ion concentrationthe OH − ion concentration is smaller than the H+ ion concentration24%the OH − ion concentration is greater than the H+ ion concentrationthe OH − ion concentration is greater than the H+ ion concentration19%the OH − ion concentration is equal of the H+ ion concentrationthe OH − ion concentration is equal of the H+ ion concentration28%Such solution doesn't existSuch solution doesn't exist27%Created by: Paweł Kołodziejczyk. Statistics based on 1745 answers in 2 languages »numbers riddles » Which of the following Roman numerals stands for 4?Both IV and IIII. Both notations are correct and historically Roman numerals were often written less consistently than today. The notation 'IIII' is often seen on clock faces. The reason for that may be practical, to avoid confusing the IV and VI when the clock is held upside down (although other theories also exist).very hard 28% IVIV68%IIIIIIII1%Both IV and IIIIBoth IV and IIII28%None of the aboveNone of the above1%Created by: globalquiz.org. Statistics based on 3204 answers in 4 languages »ancient Rome riddles » During a full 24-hour day, how many times would the hands of a clock overlap?22. The minute hand makes 24 revolutions, while the hour hand makes 2 revolutions.very hard 31% 666%121221%222231%242440%Created by: globalquiz.org. Statistics based on 5515 answers in 2 languages »time riddles » 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 38% 191938%202036%212119%80805%Created by: Gizem İsmailoğlu. Statistics based on 11173 answers in 4 languages »calendar riddles » 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 43% 20209%242443%252542%1001004%Created by: ex-terminator. Statistics based on 9091 answers in 2 languages »math riddles » 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 43% by approx 6 metersby approx 6 meters43%by approx 6 kilometersby approx 6 kilometers17%by approx 60 kilometersby approx 60 kilometers21%by approx 6000 kilometersby approx 6000 kilometers17%Created by: SpikeMe. Statistics based on 12538 answers in 2 languages »Earth riddles » 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 47% Albert EinsteinAlbert Einstein47%Blaise PascalBlaise Pascal17%Isaac NewtonIsaac Newton17%all of the aboveall of the above17%Created by: globalquiz.org. Statistics based on 7791 answers in 4 languages »scientists riddles » How many possible code combinations are there for this kind of lock?10000. The possible codes are from 0000 to 9999 inclusive.hard 50% 9999995%100010006%9999999937%100001000050%Created by: Teddy. Statistics based on 8134 answers in 2 languages »bicycles riddles » Which of the following numbers is the greatest?1/3. Quite surprisingly, most players answer that both answers 1/3 and 33% are correct. But 1/3 is more than 33%. (it is 33.3333333...)hard 52% 1/31/352%0,30,34%33%33%9%Both answers 1/3 and 33% are correctBoth answers 1/3 and 33% are correct33%Created by: globalquiz.org. Statistics based on 9132 answers in 2 languages »numbers riddles » What is the next number in the sequence? 2,3,5,7,11,13...17. The sequence 2,3,5,7,11,13 includes prime numbers only. Many people incorrectly select 15, fooled by the fact that all prime numbers except 2 are odd.hard 54% 151535%171754%19195%21213%Created by: Kasia. Statistics based on 9843 answers in 2 languages »technology riddles » Play mathematics quiz and see all the questions.