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Middle School Math
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Decimals
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 1 In the Bigtown environmental studies lab, a technician is analyzing water from the local river. She is measuring the pesticide concentration in the water. She analyzes the sample 3 times and the pesticide concentration measurements are 0.06 mg/ml, 0.08 mg/ml and 0.13 mg/ml. What was the average of the three measurements? Round your answer to the nearest thousandth.
 2 Four cross sections of petrified wood are measured. Their average diameter is 18.6 cm. Three specimens' actual diameters are 14.2, 16.7, and 15.7 cm. What must the diameter of the other specimen be?
 3 John and Kelly are counting bubbles during their yeast fermentation experiment. According to the method, the number of bubbles passing through the apparatus per second indicates the rate of sugar consumption by the yeast. During their calibration step they each counted bubbles. John counted 64 bubbles in one minute. Kelly counted 95 bubbles in 91 seconds. Compare their calculated bubble-rates (in bubbles/second) and report which one was greater, (Joshua's or Rachel's) and by how much.
 4 If, through the mechanism of continental drift, a land mass moves at an average rate of 8.62 cm per year, how many meters can it be expected to move in 4,140 years? Round your answer to the nearest hundredth.
 5 Seafloor rocks from a secret area above the Arctic Circle were recently analyzed by Z-Globe. The company had a contract with Spacegov.biz to test the rocks for nickel. Z-Globe found that four samples from the first location were composed of an average of 8.18% nickel. Nine samples from the second location yielded an average of 8.86% nickel. What was the overall average nickel content of the rock samples? Round your answer to the nearest hundredth. (Remember it is not the average of the two averages.)
 6 Two different rocks from near a recent volcanic eruption are compared. Sample A is a rock with a mass of 560 grams and a volume of 343 cm3, and sample B has a mass of 905 grams and a volume of 507 cm3. Which sample is denser and by how much? Round your answer to the nearest hundredth.

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