Which of the following numbers will completely divide
2⁶¹ + 2⁶² + 2⁶³ + 2⁶⁴?
​(a)100
(b) 10
​(c)27
​(d)17

(2⁶¹ + 2⁶² + 2⁶³ + 2⁶⁴) = 2⁶¹ x (1 + 2 + 2² + 2³) = 2⁶¹ x 15

     = 2⁶⁰ x (2 x 15)

     = (2⁶⁰ x 30), which is divisible by 10.

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