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Math Stumper


.
A
A
C
D
9
B
C
C
A
9
C
D
D
D
15
D
D
A
A
10
10
12
11
?

Answer :
The answer is 10 
d+a+d+a = ?

We know that  :
a+b+c+d = 10
a+b+c+d = a+a+d+d = 10
a+b+c+c = a+a+c+d = 9

If a+b+c+d = 10
and a+a+c+d = 9
Therefore b-a=1 (or b = a+1)

Replace
If a+b+c+c=a+a+c+d
And b = a+1
Therefore
a+a+c+c+1=a+a+c+d
Also
c+d+1=d+d
c+1=d (ou d=c+1)

Let's try.
We know that a+1= b, and c+1=d and a+b+c+d=10
Therefore
1+2+3+4=10 ?
10=10, yes.
a+1=b ?
1+1=2, yes
c+1=d?
3+1=4, yes.

Therefore : d+a+d+a = 4+1+4+1 = 10





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