text: Hi, \n\nFor the example that you gave, the number that you choose will have two digits, a and b. \n\nso the two digit number will be 10a +b. For example 23 = 10*2 + 3.\n\nThen if you add the two digits together \n(a+b) \n\nand then subtract them from the original number\n\n10a + b - (a+b) = 10a + b - a - b = 9a\n\nas you may remember, for any number times 9, if you add the digits together, you get nine. \n\n9*1 = 9\n9*2 = 18 = 1 + 8 = 9. \n9*3 = 27 = 2 + 7 = 9 \net cetera.\n\nYour answer will always be 9. It's a trick. \n\nHope that helps, \nMatt