I am a number less than 1000. The sum of my first and last digits is 8. When I am written in the reverse order, my new number is 16 less than three times the original number. If my middle digit is zero. What number am I?
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Since it is a number less than 1 0 0 0 and has a middle digit, it is a three digit number.
Numbers are either in ones, tens, hundreds, thousands, etc.
Since this is a three digit number, it is written in hundreds, tens and ones. For example, 1 2 1 can be written as 1 0 0 + 2 0 + 1 . In other words, 1 0 0 ( 1 ) + 1 0 ( 2 ) + 1 . 3 5 6 can also be written as 3 0 0 + 5 0 + 6 . In other words, 1 0 0 ( 3 ) + 1 0 ( 5 ) + 6 .
Let our three digit number be represented by x y z . Meaning it could also be written as 1 0 0 ( x ) + 1 0 ( y ) + z .
Remember that x + z = 8 .
When I am written in the reverse order, my new number is 16 less than three times the original number. That is,
z y x = 3 × ( x y z ) − 1 6 . In other words,
1 0 0 ( z ) + 1 0 ( y ) + x = 3 ( 1 0 0 ( x ) + 1 0 ( y ) + z ) − 1 6
Since the middle digit, y , is zero, we are left with
1 0 0 ( z ) + x = 3 ( 1 0 0 ( x ) + z ) − 1 6
1 0 0 ( z ) + x = 3 0 0 ( x ) + 3 ( z ) − 1 6
9 7 ( z ) = 2 9 9 ( x ) − 1 6
From the equation, x + z = 8 , we have x = 8 − z
Placing this in the equation, 9 7 ( z ) = 2 9 9 ( x ) − 1 6
We have 9 7 ( z ) = 2 9 9 ( 8 − z ) − 1 6
9 7 ( z ) + 2 9 9 ( z ) = 2 3 9 2 − 1 6
3 9 6 ( z ) = 2 3 7 6
z = 6
Placing this in the equation, x + z = 8
x = 2
Therefore, the number is 2 0 6