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unit digit problem

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unit digit problem

by didieravoaka » Thu Mar 03, 2016 4:28 pm
Does someone can explain to me what do they call "place value" in that problem? Also, I'm struggling with the units, ten and hundreds digits.

Finally, I don't understand why do they didn't keep the same direction for 7,8,9 as they did for 4,5,6.

Thanks.

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by GMATGuruNY » Thu Mar 03, 2016 5:27 pm
The sum looks as follows:

LMN
NOP
QRS

Since every digit must be used exactly once, the sum will be MINIMIZED if the blue digits are AS SMALL AS POSSIBLE and the red digits are AS BIG AS POSSIBLE, as in the following case:

1M7
2O8
3R9

Thus, the remaining 3 digits must be 4, 5, and 6:

147
258
369
774

The correct answer is C.
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by didieravoaka » Thu Mar 03, 2016 6:01 pm
Waouuh! I like it.

Thank you very much Mitch!

I will follow the same logic when I will encounter a similar case.

Marc.
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by Matt@VeritasPrep » Fri Mar 04, 2016 3:14 pm
The key takeaway here is the idea: if we're going to minimize a sum, where will we have the most impact? Here it's the 100s places, so we want those to be the smallest, etc.
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