Multiply me by any single-digit positive integer, and the sum of the digits in your product will always collapse back down to me. Which non-zero digit am I?
9
The digital root of any multiple of 9 is always 9 (e.g., 9 * 7 = 63, and 6 + 3 = 9).
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Easy. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
More math riddles
Max has 4 sleds. Noah has twice as many. How many sleds do they have together?
I am an even number strictly between 20 and 30. The sum of my digits is a perfect square. What number am I?
One dinner roll costs 3 dollars. How many dollars do 8 dinner rolls cost?
Ben puts 6 snowmen in each of 4 boxes. How many snowmen is that altogether?
Half of the 20 pencils on the table are taken away. How many pencils are left on the table?
An antique wall clock chimes once at half past every hour, and on the hour it strikes the exact number of times matching the hour (e.g., three strikes at 3:00). Starting at 1:00 AM and ending right after the strikes of 1:00 PM, how many total strikes and chimes will the clock produce?