All multiples of 9 below 90 have their digits add up to 9. amirite?

All multiples of 9 do if you repeat the process until there is only one digit, and all numbers which have this property are divisible by 9. Take 4473 for example, is that divisible by 9? 4+4+7+3 = 18, 1+8 = 9, so yes

by Emergency_Sun 3 days ago

Its actually a really easy way to tell if something is divisible by three. Add up the digits, if THAT number is divisible by 3, so is the original For instance, 57, doesnt look like it, but 5+7 = 12 12 is divisible by 3, so that means 57 is too.

by hilllelyse 3 days ago

11x9

by Anonymous 3 days ago

is 99, 9+9 is 18, 18/9 is 2

by Anonymous 3 days ago

11x9 (with extra steps) gets you to a multiple of 9. Sure.

by Anonymous 3 days ago

What exactly are you trying to say? I'm confused

by Anonymous 3 days ago

That LITERALLY all multiples of 9 adding up to 9 is factually incorrect.

by Anonymous 3 days ago

A "multiple" of a number is a number which can be divided by a number a certain whole number of times without any leftover. 12 is a multiple of 36, because 36 can be divided by 12 3 times. 99, which is a multiple of 9 (by 11) has digits which add up to 18. 18 is divisible by 9.

by Anonymous 3 days ago

They're saying that they've never played "9 Hours, 9 Persons, 9 Doors".

by Zoie27 2 days ago

99

by According_Baby 2 days ago

9+9=18 1+8=9

by Anonymous 2 days ago

6? 2 * 6 = 12, 1+2 = 3. What am I missing?

by Emergency_Sun 2 days ago

Hmm perhaps I was the one who missed something It is NOT in fact true about 6

by Anonymous 2 days ago

Learned this from schoolhouse rock. Talks about it at 2:30. The digit sum. This series just had so many nuggets of information. No wonder they beat out Sesame Street a couple of times for awards.

by Anonymous 2 days ago

This is something you learn in like 4th grade as a trick to quickly memorize multiples of 9.

by Spencerisrael 2 days ago

"All multiples of 9 below 90..." is incorrectly worded. All multipes of 9 below 99 because 9+0=9. It's all multiples below 99, though you can add a step to get to 9 with that as well.

by Anonymous 2 days ago

That's why they can show kids how to do their multiples of 9s on their fingers when they have a tough time remembering.

by SectionDecent8335 2 days ago

It's not just the ones below 90, it's literally EVERY multiple of 9. Do they not teach this in elementary school any more? Although I will admit I probably learned this from Square One's Nine Nine Nine song.

by Educational_Play 2 days ago

We were taught this in grade school. You can use your fingers to do the math. You put your hands out in front of you and put a finger down for what number you want to multiply by 9. For example for 9x3 you put your middle finger on the left down which leaves 2 fingers to the left and 7 to the right. So 9x3 is 27.

by Anonymous 2 days ago

9 x 91 = 819 -> 8+1+9 = 18 -> 1 + 8 = 9 Its all multiples of 9

by Anonymous 2 days ago