Write the equality and two conversion factors, and identify the numbers as exact or give the number of significant figures for each of the following:
b. The Daily Value (DV) for selenium is 70. mcg.

Verified step by step guidance

1. Step 1: Write the equality based on the given information. The Daily Value (DV) for selenium is 70 micrograms (mcg). The equality can be expressed as: 1 DV = 70 mcg.
2. Step 2: Create two conversion factors from the equality. Conversion factors are ratios that allow you to convert between units. The first conversion factor is (1 DV / 70 mcg), and the second conversion factor is (70 mcg / 1 DV).
3. Step 3: Identify whether the numbers in the equality are exact or measured. The number '1' in '1 DV' is exact because it is a defined quantity. The number '70' in '70 mcg' is measured, and its significant figures need to be determined.
4. Step 4: Determine the number of significant figures in the measured value '70 mcg'. Since '70' does not have a decimal point, it has 2 significant figures.
5. Step 5: Summarize the equality, conversion factors, and the classification of numbers. The equality is 1 DV = 70 mcg, the conversion factors are (1 DV / 70 mcg) and (70 mcg / 1 DV), the number '1' is exact, and '70' has 2 significant figures.

Key Concepts

Daily Value (DV)

The Daily Value (DV) is a reference value used on food labels to indicate how much a nutrient in a serving of food contributes to a daily diet. It is based on a daily intake of 2,000 calories and helps consumers understand the nutritional content of food in the context of a total daily diet. For selenium, the DV is set at 70 micrograms (mcg), which reflects the recommended daily intake for adults.

Conversion Factors

Conversion factors are numerical values used to convert one unit of measurement to another. In the context of the DV for selenium, conversion factors can be used to express the amount in different units, such as milligrams (mg) or grams (g). For example, 1 mcg is equal to 0.001 mg, and knowing these factors is essential for accurate dietary calculations and comparisons.

Significant Figures

Significant figures are the digits in a number that contribute to its precision, including all non-zero digits, any zeros between significant digits, and trailing zeros in the decimal portion. In the case of the DV for selenium, the number 70 mcg is considered to have two significant figures. Understanding significant figures is crucial for accurately reporting measurements and ensuring that calculations reflect the precision of the data.