# Math Is Fun Forum

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## #1 2022-08-24 04:52:39

Abbey78336
Member
Registered: 2022-08-15
Posts: 37

### What is the number?

The sum of A number and the sum of its digits is 379. What is the number???????????

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## #2 2022-08-24 05:03:40

phrontister
Real Member
From: The Land of Tomorrow
Registered: 2009-07-12
Posts: 4,818

### Re: What is the number?

Edit:
I deleted my answer, which was just the number.
I posted it very prematurely without giving any help at all, despite this being the Help Me! forum.
>blush<

Last edited by phrontister (2022-09-09 11:44:18)

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## #3 2022-08-24 05:12:47

Abbey78336
Member
Registered: 2022-08-15
Posts: 37

### Re: What is the number?

From where? Step by step

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## #4 2022-08-24 05:58:01

zetafunc
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Registered: 2014-05-21
Posts: 2,432
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## #5 2022-08-24 06:09:02

Abbey78336
Member
Registered: 2022-08-15
Posts: 37

Another one

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## #6 2022-08-24 06:30:31

Bob
Registered: 2010-06-20
Posts: 10,153

### Re: What is the number?

hi Abbey,

This is what I did to solve this.

Suppose the number is abc where a is the number of hundreds, b the number of tens, and c the remaining units. All three must be singkle digit numbers ie from the set {0,1,2,3,4,5,6,7,8,9}

To express this correctly using algebra you have to find a way to show that the 'a' is worth 'a' hundreds and the 'b' is worth 'b' tens.  So you write the number as 100a + 10b + c.  Doing this makes sure that the correct place value is applied to the hundreds and the tens.

We also have to add on the actual digits so the total becomes 100a + 10b + c + a + b + c = 101a + 11b + 2c = 379

Now the only way you could get to 3 hundred and something is if a = 3.  Less than 3 and the total would be under 300. More than that and the total would be over 400.  So a= 3 is forced upon us.

So subtract 3a = 303 and the equation becones 11b + 2c = 379 - 303 = 76

Now you can apply a similar logic to determine 'b'.  If it were b = 7 the equation would be 77 + 2c = 76. That cannot be right, as c would have to be negative.

And if it were only b = 5 the equation would be 55 + 2c = 76 and yet 'c' is 9 or less so that doesn't work either.

So b is forced to be ?  I'll leave you to finish this off from here.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #7 2022-08-24 21:39:59

Abbey78336
Member
Registered: 2022-08-15
Posts: 37

### Re: What is the number?

So we will use 6 giving 66+2c=76 c=5 and we know that a=3 b=6 c=5 abc=365.
AS SIMPLE AS DYING

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