Riddle! Riddle! #2

Algebra Level 2

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?


The answer is 206.

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1 solution

Nehemiah Osei
Aug 27, 2015

Since it is a number less than 1000 1000 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, 121 121 can be written as 100 + 20 + 1 100+20+1 . In other words, 100 ( 1 ) + 10 ( 2 ) + 1 100(1)+10(2)+1 . 356 356 can also be written as 300 + 50 + 6 300+50+6 . In other words, 100 ( 3 ) + 10 ( 5 ) + 6 100(3)+10(5)+6 .

Let our three digit number be represented by x y z xyz . Meaning it could also be written as 100 ( x ) + 10 ( y ) + z 100(x)+10(y)+z .

Remember that x + z = 8 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 ) 16 zyx=3 \times (xyz)-16 . In other words,

100 ( z ) + 10 ( y ) + x = 3 ( 100 ( x ) + 10 ( y ) + z ) 16 100(z)+10(y)+x=3(100(x)+10(y)+z)-16

Since the middle digit, y y , is zero, we are left with

100 ( z ) + x = 3 ( 100 ( x ) + z ) 16 100(z)+x=3(100(x)+z)-16

100 ( z ) + x = 300 ( x ) + 3 ( z ) 16 100(z)+x=300(x)+3(z)-16

97 ( z ) = 299 ( x ) 16 97(z)=299(x)-16

From the equation, x + z = 8 x+z=8 , we have x = 8 z x=8-z

Placing this in the equation, 97 ( z ) = 299 ( x ) 16 97(z)=299(x)-16

We have 97 ( z ) = 299 ( 8 z ) 16 97(z)=299(8-z)-16

97 ( z ) + 299 ( z ) = 2392 16 97(z)+299(z)=2392-16

396 ( z ) = 2376 396(z)=2376

z = 6 z=6

Placing this in the equation, x + z = 8 x+z=8

x = 2 x=2

Therefore, the number is 206 206

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