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Question:

The unit digit in (743)⁸⁵ – (525)³⁷ + (987)⁹⁶ is ________

Explanation:

Unit's digit of (743)⁸⁵ = Unit's digit of 3⁸⁵ 
= Unit's digit of (3⁴)²¹ × 3 = 1 × 3 = 3 [Unit's digit of 3⁴ = 1]

Units's digit of (525)³⁷ = Units's digit of 5³⁷ = 5

Units's digit of (987)⁹⁶​​​​​​​ = Units's digit of 7⁹⁶ 
= Units's digit of (7⁴)²⁴ = 1 [Unit's digit of 7⁴ = 1]

∴ Unit's digit of (743)⁸⁵ – (525)³⁷ + (987)⁹⁶ = 3 - 5 + 1 = -1 = 9

Hence, option (a).