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1. Imagine a number that is greater than 1 , and keep it in your mind.

2.Multiply that number by 9 and keep the result in your mind.

3.Now, sum the digits of your result.

OK. Let me read your mind..........Yes, the answer in your mind is "9". Sounds crazy? Emotion: smile
1 2
Comments  
this is simple

for any number to be divided by 9 ,the sum of its digits must be 9 or something divided by 9 too

try to multiply any number by 9 and then add the digits of the result all together Emotion: big smile

same rule applied for 3. any number to be divided by 3 the sum of its digits must be 3,6,9, or anything dividable by 3

good one here

[Y]
Tattyjackythis is simple

for any number to be divided by 9 ,the sum of its digits must be 9 or something divided by 9 too

try to multiply any number by 9 and then add the digits of the result all together Emotion: big smile

same rule applied for 3. any number to be divided by 3 the sum of its digits must be 3,6,9, or anything dividable by 3

good one here

[Y]

Perfect. You got the key, Tatty.
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congratulations:)
RishonlyPerfect. You got the key, Tatty.
In fact, Tattyjacky and Rishonly, that's the quick trick we use to test a number's divisibility by 9. Emotion: big smile Used it since I was eight years old, in factEmotion: smile

Cheers!

- Joy

[f]
Tearsofjoy
RishonlyPerfect. You got the key, Tatty.
In fact, Tattyjacky and Rishonly, that's the quick trick we use to test a number's divisibility by 9. Emotion: big smile Used it since I was eight years old, in factEmotion: smile

Cheers!

- Joy

[f]

So, you are quite powerful in Math for seven years, TJ.
Students: Are you brave enough to let our tutors analyse your pronunciation?
Nope, Rishonly, it was taught to us in school! Emotion: smile

Here are the divisibility keys that I know -

2 - last digit is an even number

3 - sum of the digits is a multiple of 3. If that number is too long, then sum the digits again and again till you get to a 2-digit or 1-digit number.

4 - last two digits are divisible by 4.

5 - last digit is 5 or 0.

6 - it has to be divisible by 2 and 3(obviously)

7 - none that I know of

8 - last 3 digits are divisible by 8.

9 - sum of the digits add up to 9.

There is one for 11, but it's complicated. I've forgotten it. Emotion: embarrassed. Anyway, division by 11 is easy Emotion: wink

Cheers,

- Joy

Emotion: geeked
Courtesy of http://www.jimloy.com/number/divis.htm , we have -

Divisibility test for 11 - The difference between the sum of the odd numbered digits (1st, 3rd, 5th...) and the sum of the even numbered digits (2nd, 4th...) is divisible by 11.

There's a test for 7 in there too, but I found it really complex. I'd rather divide by 7, thanks!

Cheers,

- Joythegeek.
1. think of a number?

2. double the number?

3. add 100?

4. half the number?

5. take away the number you started with?

6. is your answer 50?
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