1.

1). 52). 03). 34). 9

Answer»

As, 5! = 1 × 2 × 3 × 4 × 5 will have 0 as its unit digit because of the presence of (2 × 5). HENCE all factorials above it will have 0 as their unit digit

⇒ 1! + 2! + 3! + 4! = 1 + 2 + 6 + 24 = 33

∴ Unit digit of (1! + 2! + 3! + 4! + _________ + 20!) = Unit digit of (1! + 2! + 3! + 4!) = 3



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