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The sum of the digits of a two digit number is 12. If 18 is added to it, the digits are reversed. Wh

 
 
Reply Fri 28 Feb, 2014 07:06 am
The sum of the digits of a two digit number is 12. If 18 is added to it, the digits are reversed. What is the number?
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Type: Question • Score: 3 • Views: 4,453 • Replies: 9

 
Lordyaswas
 
  1  
Reply Fri 28 Feb, 2014 07:31 am
@Abhi2610,
OK, this is obviously homework, so I will only give you the first hint or two.

1. Work backwards.(hint1)
2. What is the lowest number where the three (hint 2) digits add up to 21?

Presto Hey!
0 Replies
 
DrewDad
 
  1  
Reply Fri 28 Feb, 2014 07:35 am
@Abhi2610,
Make a chart of two digit numbers that add up to 12. Make a second column and add 18.
0 Replies
 
engineer
 
  2  
Reply Fri 28 Feb, 2014 09:59 am
@Abhi2610,
X = first digit
Y = second digit

X + Y = 12
10X + Y + 18 = 10Y + X

Solve for X and Y
Lordyaswas
 
  1  
Reply Fri 28 Feb, 2014 03:04 pm
This must be an age thing.

I looked at this problem/question, and immediately did it all in my head without lists, x's and y's, and it took about ten seconds.

When I was at school aged eight or nine ( beatles, spam fritters, jumpers for goalposts) we had a Maths teacher who gave us this sort of problem all the time, and we had to work it all out in our heads if at all possible.

Algebra is great, and lists are very logical, but doesn't anyone work anything out in their heads any more?
timur
 
  3  
Reply Fri 28 Feb, 2014 03:13 pm
It isn't an age thing, I know plenty of young people that still do it.

I also know a lot of old airheads.

(Should I give names?)
Lordyaswas
 
  1  
Reply Fri 28 Feb, 2014 03:19 pm
@timur,
If that's the case, Timur, then all is still right with the world,

It would be nice to think that the 'mental' element isn't being ignored.
0 Replies
 
contrex
 
  -1  
Reply Sat 1 Mar, 2014 07:58 am
@Lordyaswas,
Lordyaswas wrote:
it took about ten seconds.

It's a piece of piss. The only 2 digit numbers whose digits when added make 12 are 39, 48, 57, 66, 75, 84 and 93. The last two we can rule out because adding 18 to either would give a 3 digit number. So mentally add 18 to the others until you find the right one. In fact if you look at them, either in your mind's eye or on paper, you can see which is the right one. At least I can.



0 Replies
 
DrewDad
 
  1  
Reply Sat 1 Mar, 2014 10:42 am
@engineer,
engineer wrote:

X = first digit
Y = second digit

X + Y = 12
10X + Y + 18 = 10Y + X

Solve for X and Y

This made me laugh.... I've been working too much in spreadsheets.
0 Replies
 
JessicaWatson014
 
  1  
Reply Wed 16 Apr, 2014 03:18 am
Its so simple 57 is the answer . add 18 to 57 will give 75 which is reversed of 57.
5 +7 = 12
0 Replies
 
 

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