Express the number 554,780,000,040 in scientific notation to three significant figures.

A recent study found that the median concentration of lead in Canadian tap water is 2.3 x10-8 mol/L. Calculate the mass, in grams, of lead consumed when an individual drinks 3.0 L of water. You must show your work.  Then, record your final answer in scientific notation, with the correct number of significant digits and proper units.

What is the mass, in grams, of 28.74 mLmL of acetone? Express your answer using four significant figures.

Calculate the volume of 42.0 kg of a substance whose density is 8.96 g/mL. Express your answer in milliliters using the correct number of significant figures. Do not enter your answer using scientific notation.

If the area of one tile is measured to be 1.07 ft2, how many tiles do you need to redo the floor of a 10.1 ft x 12.07 ft bathroom? Write the answer in the correct number of significant figures?

(282.7×105)−(1.100×103)]×2.8990 Express your answer to the appropriate number of significant digits.

A student sets up the following equation to convert a measurement. (The ? stands for a number the student is going to calculate.) Fill in the missing part of this equation. (84. cm )· 0= ? m² 3 3

In 1999, scientists discovered a new class of black holes with masses 100 to 10,000 times the mass of our sun, but occupying less space than our moon. Suppose that one of these black holes has a mass of 1×10^3 suns and a radius equal to one-half the radius of our moon. What is its density in grams per cubic centimeter? The mass of the sun is 2.0×10^30 kg and the radius of the moon is 2.16×10^3 mi (Volume of a sphere =4/3πr^3)

1.19×10^−8s to nanoseconds Express your answer to three significant figures and include the appropriate units.

A chemistry student needs 35.0 mL of dimethyl sulfoxide for an experiment. By consulting the CRC Handbook of Chemistry and Physics, the student discovers that the density of dimethyl sulfoxide is 1.10 g·cm -3 Calculate the mass of dimethyl sulfoxide the student should weigh out. Be sure your answer has the correct number of significant digits. ?