To arrange the decimals from least to greatest, let's compare each of the given sets:
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1.9, 1.09, 1.009:
- 1.009 < 1.09 < 1.9
- Order: 1.009, 1.09, 1.9
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1.99, 1.9, 1.09:
- 1.09 < 1.9 < 1.99
- Order: 1.09, 1.9, 1.99
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1.9, 1.091, 1.09:
- 1.09 < 1.091 < 1.9
- Order: 1.09, 1.091, 1.9
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1.09, 1.9, 1.92:
- 1.09 < 1.9 < 1.92
- Order: 1.09, 1.9, 1.92
The only set that is correctly ordered from least to greatest is 1.09, 1.9, 1.92.
So the correct answer for the order from least to greatest is: 1.09, 1.9, 1.92.