Question 1126865
Here is a multiplication involving two 16-digit numbers:

3851902343886132x5221791683705111

The 32-digit product is 20 113 831 625 748 8_8 690 240 050 420 652

What is the missing digit in the product?
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3851902343886132*5221791683705111
Using excess of 9's, or "casting out 9's" - I forget what it's called:
--> 3*5 = 15 --> 6
20 113 831 625 748 8_8 690 240 050 420 652 --> 4
The missing digit is 2.