10 most difficult numbers riddles A list of numbers related questions that are most often answered incorrectly Numbers 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 2348 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 29% IVIV67%IIIIIIII1%Both IV and IIIIBoth IV and IIII29%None of the aboveNone of the above1%Created by: globalquiz.org. Statistics based on 3923 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 9708 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 44% 20209%242444%252541%1001004%Created by: ex-terminator. Statistics based on 11140 answers in 2 languages »calendar riddles » Which currency was the first to be converted to decimal system?Russian ruble. The new ruble introduced with monetary reform of Peter the Great of 1704 was the first currency to be based on decimal system.hard 45% American dolarAmerican dolar17%British pound sterlingBritish pound sterling16%frank of revolutionary Francefrank of revolutionary France20%Russian rubleRussian ruble45%Created by: smyru. Statistics based on 745 answers in 2 languages »coins 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% 3320%4450%121222%40406%Created by: Sumit Tamang. Statistics based on 7216 answers in 4 languages »South Korea riddles » What is the sum of all the numbers on the roulette wheel?666. This fact contributed to the naming of the game as Satan one, since 666 it is called the number of the beast by the Book of Revelation.hard 52% 6006008%66666652%78378322%1000100017%Created by: smyru. Statistics based on 2154 answers in 2 languages »games 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 54% 1/31/354%0,30,34%33%33%9%Both answers 1/3 and 33% are correctBoth answers 1/3 and 33% are correct31%Created by: globalquiz.org. Statistics based on 12524 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 54% 5533%7754%998%11113%Created by: Paweł Kołodziejczyk. Statistics based on 5483 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 8878 answers in 2 languages »geometry riddles » Play numbers quiz and see all the questions.