A number magician tells you: Pick any postive integre and mutiply it by 18. Delete one of the non-zero digits of the poduct.Tell me the sum of the remaning digits of the product and I will tell you what digit you deleted.Explainthis trick.
A number magician tells you: Pick any postive integre and mutiply it by 18. Delete one of the non-zero digits of the poduct.Tell me the sum of the remaning digits of the product and I will tell you what digit you deleted.Explainthis trick.
Any multiple of 9 will have a sum of digit that is divisible 9.
18 is divisible by 9.
So when you are looking at multiple of 18 - it is a multiple of 9 too.
Thus multiple of 18 will have "sum of digits" divisible by 9.
suppose you chose 18 * 43 = 774
and you decide to drop 4 - so sum of remainig digit is 14.
You must have started from a sum-of-digit of 18 - so you must have dropped 4.
Try other numbers say 18 * 69 = 1242
You decide to drop '4' and give me the sum '5'
You must have started from '9' and you have dropped '4' (= 9-5)
Interactive Math Goodies Software
Math grade 8
Posted - 09/25/2009 : 19:44:38
