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Decimal notation is a way of expressing numbers that have parts smaller than the whole, which we refer to as fractions or decimals. The system is based on powers of ten, making it simple yet powerful for representing numbers both large and small. In this notation, each position to the right of the decimal point represents a negative power of ten.

For example, in the decimal 39.9, the digit 9 to the right of the decimal point is in the tenths place, which means it is multiplied by 1/10 or 0.1. If there were another number to the right, say 39.95, the second digit after the decimal point would represent the hundredths place, multiplied by 1/100 or 0.01. It's essential to understand decimal notation as it's commonly used in mathematics, science, and everyday life for precision and clarity.

Place value is crucial in understanding how numbers are constructed in our decimal numeral system. Each position in a number has a different value, determined by the base of the numeral system, which is ten for decimals. With reference to place value, each digit in a number has a specific 'place,' such as the units place, the tens place, the hundreds place, and so on. This extends beyond the decimal point to the tenths place, hundredths place, and further.

For instance, in the number 39.9 mentioned in the exercise, 3 is in the tens place, 9 is in the units place, and the final 9 is in the tenths place. Understanding the place value is vital for converting words to decimals correctly, as it indicates the magnitude of each digit within the number.

Converting fractions to decimals is a foundation skill in mathematics. To successfully convert a fraction, such as nine tenths, you need to divide the numerator by the denominator. This action gives us a decimal that shows the same value as the fraction.

In the example of converting nine tenths to a decimal, we simply divide 9 by 10 to get 0.9. Other, more complicated fractions might require more steps to convert, but the principle remains the same: it is a division process. Knowing how to convert fractions to decimals is particularly helpful in real-world scenarios, such as when dealing with finances or measurements, where decimal notation is typically the standard form of expression.