10 most difficult numbers riddles A list of numbers related questions that are 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 25% the OH − ion concentration is smaller than the H+ ion concentrationthe OH − ion concentration is smaller than the H+ ion concentration25%the OH − ion concentration is greater than the H+ ion concentrationthe OH − ion concentration is greater than the H+ ion concentration20%the OH − ion concentration is equal of the H+ ion concentrationthe OH − ion concentration is equal of the H+ ion concentration27%Such solution doesn't existSuch solution doesn't exist26%Created by: Paweł Kołodziejczyk. Statistics based on 2176 answers in 2 languages »mathematics 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 3701 answers in 4 languages »ancient Rome riddles » Which numeral system was in use in ancient Sumer and Babilon?Sexagesimal. Remnants of highly composite sexagesimal system are in use even today for measuring angles, geographic coordinates and especially time. An hour of time is divided into 60 minutes, which in turn are divided into 60 seconds. very hard 32% octaloctal21%binarybinary19%decimaldecimal25%sexagesimalsexagesimal32%Created by: smyru. Statistics based on 9363 answers in 2 languages »ancient history 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 10540 answers in 2 languages »calendar riddles » Which number is considered unlucky in East Asia?4. Words "four" and "Death" have very similar pronunciation in Chinese, Vietnamese, Korean and Japanese. In East Asia many buildings do not have a 4th floor. Some high-rise residential buildings omit all floor numbers with "4", e.g., 4, 14, 24, 34 and all 40–49 floors. hard 50% 3321%4450%121222%40406%Created by: Sumit Tamang. Statistics based on 6794 answers in 4 languages »South Korea 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 53% 1/31/353%0,30,34%33%33%9%Both answers 1/3 and 33% are correctBoth answers 1/3 and 33% are correct32%Created by: globalquiz.org. Statistics based on 11394 answers in 2 languages »mathematics riddles » How many players of one team are there in a pool during the water polo game?7. A team consists of 6 field players and one goalkeeper in the water at any one time. hard 53% 5533%7753%999%11113%Created by: Paweł Kołodziejczyk. Statistics based on 4967 answers in 2 languages »water riddles » What is the volume of a soap bubble with radius R=1 cm?4/3π cm3. Equation for the volume of a sphere: 4/3πR^3.hard 58% 3/4π cm33/4π cm319%4/3π cm34/3π cm358%4,3π cm34,3π cm310%It isn't possible to calculateIt isn't possible to calculate11%Created by: Paweł Kołodziejczyk. Statistics based on 8172 answers in 2 languages »geometry riddles » 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% 23882990238829909%167690231676902366%38377296383772968%117238351172383515%Created by: Sumit Tamang. Statistics based on 11779 answers in 2 languages »math riddles » Which pH number describes a substance that is neither acidic nor alkaline?PH 7. Solutions with a pH value below 7.0 are considered acidic, whereas solutions with pH values above 7.0 are basic.easy 70% pH 0pH 019%pH 7pH 770%pH 10pH 104%pH 0.5pH 0.55%Created by: Cleo. Statistics based on 10284 answers in 2 languages »chemistry riddles » Play mathematics quiz and see all the questions.