Which non-zero single-digit number, when multiplied by any other single-digit number, always results in a product whose digits sum up to that same number?
9
Multiples of 9 have digit sums that equal 9 (e.g., 9×2=18 -> 1+8=9; 9×5=45 -> 4+5=9; 9×9=81 -> 8+1=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: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
More math riddles
There are 18 snowmen in a box and 5 are taken out. How many snowmen are left?
In a room of 30 people, every person shakes hands with every other person exactly once. How many total handshakes take place?
I am a number with four digits. All of my digits are different. My thousands digit is three times my units digit, and my hundreds digit is the sum of my thousands and units digits. My tens digit is zero. What number am I?
Kai gets 7 calendars on Monday and 2 calendars on Tuesday, then gives away 5. How many calendars are left?
Zoe has 14 snowmen and Eli has 7. How many more snowmen does Zoe have?
There are 21 seeds in a box and 9 are taken out. How many seeds are left?