Saturday, September 27, 2014

JMO --- numbers

We have a four-digit number that is a multiple of 9. Of the four digits, three of the consecutive digits are same. How many such numbers are possible?

Answer:

if the 3 same consecutive number is "a" and the other number is 'b", then
3a + b = 9, 18, 27, 36 .... for being a multiple of 9.


           






















Therefore, 20 possible numbers

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