Calculus Online Book
Standard error of the mean
When you take a sample of observations from a population, the mean of the sample is an estimate of the parametric mean, or mean of all of the observations in the population. If your sample size is small, your estimate of the mean won't be as good as an estimate based on a larger sample size. Here are 10 random samples from a simulated data set with a true (parametric) mean of 5. The X's represent the individual observations, the red circles are the sample means, and the blue line is the parametric mean. As you can see, with a sample size of only 3, some of the sample means aren't very close to the parametric mean. You'd often like to give some indication of how close your sample mean is likely to be to the parametric mean. Here's a figure illustrating this. Usually you won't have multiple samples to use in making multiple estimates of the mean. This figure is the same as the one above, only this time I've added error bars indicating ±1 standard error. Similar statistics Example Web pages
Interactive Mathematics Miscellany and Puzzles
Particles found to break speed of light
9 Mental Math Tricks
Math can be terrifying for many people. This list will hopefully improve your general knowledge of mathematical tricks and your speed when you need to do math in your head. 1. So, 9×9 is just 9x(10-1) which is 9×10-9 which is 90-9 or 81. Let’s try a harder example: 46×9 = 46×10-46 = 460-46 = 414. One more example: 68×9 = 680-68 = 612. To multiply by 99, you multiply by 100-1. So, 46×99 = 46x(100-1) = 4600-46 = 4554. Multiplying by 999 is similar to multiplying by 9 and by 99. 38×999 = 38x(1000-1) = 38000-38 = 37962. 2. To multiply a number by 11 you add pairs of numbers next to each other, except for the numbers on the edges. Let me illustrate: To multiply 436 by 11 go from right to left. First write down the 6 then add 6 to its neighbor on the left, 3, to get 9. Write down 9 to the left of 6. Then add 4 to 3 to get 7. Then, write down the leftmost digit, 4. So, 436×11 = is 4796. Let’s do another example: 3254×11. The answer comes from these sums and edge numbers: (3)(3+2)(2+5)(5+4)(4) = 35794. 3. 4.
SpaceX Craft Docks With Space Station; Commercial Era Begins : The Two-Way
The historic first docking of a commercial spacecraft at the International Space Station orbiting above Earth happened without a hitch today, as SpaceX's Dragon capsule arrived with supplies for the crew orbiting high above Earth. Just before 10 a.m. ET, astronauts aboard the space station successfully grabbed the capsule with a robotic arm. A little after noon ET, the pulled the Dragon into its docking space. NASA was webcasting, and we have embedded its feed in this post (our apologies if you're on a device that doesn't support the player). Earlier this week on All Things Considered, NPR's Nell Greenfieldboyce reported about the historic mission. Update at 12:10 p.m. Dragon has finished docking with the International Space Station. That happened at exactly 12:02 p.m. Update at 10:40 a.m. Capturing Dragon "was a big moment for SpaceX and a big moment for NASA too," NPR's Nell Greenfieldboyce said on Morning Edition a short time ago. Update at 10:15 a.m. Update at 9:56 a.m.
Pauls Online Math Notes
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Agencies and Offices A list of all Agencies and Offices within USDA Farm and Foreign Agricultural Services Commodity, credit, conservation, disaster, emergency assistance programs... Food, Nutrition and Consumer Services Dietary guidance, nutrition policy coordination, nutrition education... Food Safety Meat, poultry, and egg inspection, food recalls, food labeling, packaging... Marketing and Regulatory Programs Organic program, animal and plant health, grain inspection... Natural Resources and Environment Forestry, conservation, damage prevention, land management, sustainable land management... Research, Education and Economics U.S. food and fibers system, library, statistics, research, analysis, education... Rural Development Financial programs, water and sewer systems, housing, health clinics, economic development, loans, lending pools...
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