Final answer:
The number 5.1×10^7 is written as 51,000,000 in decimal notation.
Step-by-step explanation:
In scientific notation, the number 5.1×10^7 is written as 51,000,000. This is because the exponent of 10 tells us how many places to move the decimal point to the right. In this case, we need to move the decimal point 7 places to the right, resulting in a value of 51,000,000.