<h3>
Answer: 21600 </h3>
==========================================================
Explanation:
There are 6 letters to pick from {A,B,C,D,E,F} and we have two slots to fill, where no repeats are allowed. This means we have 6*5 = 30 different ways to pick two letters.
There are 10 digits to pick from {0,1,2,...,9} and there are 3 slots to fill. This gives 10*9*8 = 720 different permutations for this portion.
Overall, we have 30*720 = 21600 different serial numbers possible.
Here's one way to do it.
AB ≅ AC . . . . . . . . . . given
∠BAY ≅ ∠CAY . . . . given
AY ≅ AY . . . . . . . . . . reflexive property
ΔBAY ≅ ΔCAY . . . .. SAS congruence
XY ≅ XY . . . . . . . . . . reflexive property
∠AYB ≅ ∠AYC . . . . CPCTC
BY ≅ CY . . . . . . . . . . CPCTC
ΔXYB ≅ ΔXYC . . . .. SAS congruence
Therefore ...
∠XCY ≅ ∠XBY . . . . CPCTC
U can easily put this through a calculator, but it’s 24 :)
