Respuesta :

Answer:

Step-by-step explanation:

there is an obscure rule that looks like this

DB/AB = AB/CB

AB=40 for this problem

DB = x

CB = 20

then

X/40 = 40/20

X = 40(40/20)

X = 40(2)

X=80

I find that hard to believe too,   :D

but the rule says that's right

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