1 answer
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First, let's convert all the numbers to a standard form.
3.1×10^5 = 310,000
4.5×10^5 = 450,000
3.1×10^8 = 310,000,000
6.8×10^2 = 680
Now let's put them in order from least to greatest:
680, 310,000, 450,000, 310,000,000, 730,000
The third number in the list is 450,000.