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Question

What is the unit digit in 771 ?
Options:
A .  4
B .  3
C .  2
D .  1
Answer: Option B

Answer : Option B

Explanation :

771 = (74)17 × 73
Hence, unit digit in 771
= Unit digit in [(74)17 × 73]
= Unit digit in [(7 × 7 × 7 × 7 )17 × 73]
= Unit digit in [(9 × 9)17 × 73] (∵ 7 × 7 = 49 and 9 is the unit digit of 49)
= Unit digit in [117 × 73] (∵ 9 × 9 = 81 and 1 is the unit digit of 81)
= Unit digit in [1 × 73] (∵ 117 = 1)
= Unit digit in [73]
= Unit digit in [7 × 7 × 7]
= Unit digit in [9 × 7](∵ 7 × 7 = 49 and 9 is the unit digit of 49)
= 3 (∵ 9 × 7 = 63 and 3 is the unit digit of 63)



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