Final answer:
To determine the unit rate from the given ordered pairs representing money in US dollars and euros, Option A (100, 78) is correct because it can be reduced to a unit rate of (1, 0.78), indicating one US dollar is equivalent to 0.78 euros.
Step-by-step explanation:
The ordered pairs provided show amounts of money in US dollars and euros. To find the unit rate, we need an ordered pair that shows the ratio of 1 dollar to its equivalent in euros. Looking at the options, we can see that only Option A (100, 78) can be reduced to a unit rate by dividing both the dollar amount and the euro amount by 100, resulting in the unit rate of (1, 0.78). This means that one US dollar is equivalent to 0.78 euros.
Options B, C, and D cannot represent the unit rate as they are not simplified to the basis of one dollar. For instance, Option B (150, 117) would need to be divided by 150 to get the unit rate, resulting in an incorrect ratio of (1, 0.78). Option C (1200, 156) is incorrect because when divided by 1200, it does not give a ratio of 1 dollar to its euro equivalent, and Option D (2100, 50) is incorrect since the amounts of money do not reflect the current exchange rates between US dollars and euros.