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Why is it always 1089
You will need a little bit off algebra.
But stick with it, it is not difficult.
Represent the number with
ABC
Reverse this to get
CBA
Remember that A is Hundreds B is tens and C is units
Take
CBA
from
ABC
like this
Hundreds
Tens
Units
A
B
C
C
B
A
Now here is the trick: subtract 1 Hundred, and add 9 Tens and 10 Ones (-100, +90, +10 = 0, so won't change answer):
Hundreds
Tens
Units
A-1
A
B+9
B
10+C
C
C
B
A
A-1-C
9
10+C-A
Last Step: Reverse the answer and add the two numbers together.
A-1-C
9
10+C-A
+
10+C-A
9
A-1-C
9
18
9
(simplify:)
10
8
9
As predicted the answer was 1089
Always End With 1089
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