To express the numbers in scientific notation, we need to convert each number into the form \( a \times 10^n \), where \( 1 \leq a < 10 \) and \( n \) is an integer representing the power of ten.
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For 98,789,000: \[ 98,789,000 = 9.8789 \times 10^7 \]
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For 987,890,000: \[ 987,890,000 = 9.8789 \times 10^8 \]
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For 89,987,000: \[ 89,987,000 = 8.9987 \times 10^7 \]
Now we can compare the values. The exponents tell us that:
- \( 9.8789 \times 10^7 \) is in the 10 million range,
- \( 9.8789 \times 10^8 \) is in the 100 million range,
- \( 8.9987 \times 10^7 \) is also in the 10 million range.
To directly compare \( 9.8789 \times 10^7 \) and \( 8.9987 \times 10^7 \):
- \( 9.8789 \times 10^7 \) (98,789,000)
- \( 8.9987 \times 10^7 \) (89,987,000)
Since \( 8.9987 < 9.8789 \), we can conclude that:
- \( 89,987,000 \) has the least value among the three numbers.
In summary, the number with the least value expressed in scientific notation is: \[ \boxed{8.9987 \times 10^7} \]