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how to solve this question.. any input

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Junior | Next Rank: 30 Posts
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by me4mba » Sat Oct 27, 2007 3:54 pm
The question asks for the unit digit only?

2^20 * 2^19 = 2^(20+19) = 2^39

The trick is to recognize the pattern of 2^x

2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16
2^5 = 32
2^6 = 64
2^7 = 128 ...

You can see that the unit digit of 2^x repeats every 4 increments of x.

From that, we know that 2^40 must have a unit digit of 6 and 2^39 will therefore have a unit digit of 8.
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Master | Next Rank: 500 Posts
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by ri2007 » Sat Oct 27, 2007 6:15 pm
have solved this earlier - check this link

https://www.beatthegmat.com/viewtopic.php?t=6325
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