Question 892975
Mico's house number has three digits. Removing the leftmost digit gives Ben's
house number. Removing  the leftmost digit of Ben's house number gives Ciara's
house number.  The sum of the three house numbers is 912.  What is the middle
digit of Mico's house number?
<pre>

Let h = the hundreds digit (of Mico's house number)
Let t = the tens digit 
Let u = the units digit

So the house numbers written in digit form are 

Mico's house number = htu.
Ben's house number = tu.
Clara's house number = u.

We form the arithmetic (basic math) addition:

htu
 tu
  u
---
912

In the right column To get the 2 at the bottom, the 3 u's have 
to be 4 so they'll add up to 12 and there'll be 1 to carry.  So 
we have this:

 1
ht4
 t4
  4
---
912

Looking at the middle column of digits, either the two t's are 0 
so the middle column of digits will add up to 1, or the two t's 
are 5 so that the middle column will add up to 11 with 1 to carry.
But t can't be 0 because that would make Ben's house number 04.  
But nobody writes 04, they just write 4.  So if you removed the 
leftmost digit of 4 you would have nothing at all!  So 0 is out.

Therefore t = 5  (That's the answer).

Completing the addition:

11
h54
 54
  4
---
912 

Since we have 1 to carry to the left column,
which gives us a 9 at the bottom left, h can 
only be 8.

11
854
 54
  4
---
912

The house numbers are 854, 54, and 4 and the 
middle digit of Mico's house number is 5.

Edwin</pre>