# measurement

Knot Activity Name: Procedure: Get a small string that is anywhere from 13 to 15 centimeters in length. Measure the length of your string and record the measurement in the table below. Put one knot in the string, measure the length of the string, and record the length in the table below. (Remember that the more precise you are with your measurements the better this will work) You don’t need to stretch your string super tight but stretch it straight. Number of Length of String (in Knots centimeter) 1 2 3 4 5 6 7 8 1. Graph the data by hand by placing x’s on the graph below. Make sure you label and scale your x and y-axis. 2. What is the y intercept for the data?_____________ What does the y-intercept represent in this case? 3. What type of mathematical model does the data appear to fit? 4. Draw a line through the y-intercept and through as many other points as possible. 5. Find the slope of the line you drew by picking two points on the line. 6. Write a sentence interpreting the slope in this situation. 7. Use the slope and y intercept to write the equation of the line. 8. Post your equation in the discussion and compare yours to another classmate. Are they the same? If so, why? If not, why not? 9. Now input your data into a spreadsheet and make a scatter-plot. Add a trend line to the data(in statistics it is called a line of best fit or regression line). 10. What is the slope?____________________ What is the y-intercept?____________________ 11. Write the equation of the line using the slope and y-intercept from #10. 12. How does your equation using the spreadsheet’s regression compare with the equation you wrote when you drew the line by hand? Explain. Use your equation you got from the spreadsheet to complete the following problems. 13. Graphically, the y-intercept is where the graph intersects the y-axis. It can be found by letting x=0. Use the equation to find the y-intercept. 14. Graphically, the x-intercept is where the graph crosses the x-axis. It can be found by letting y=0. Use the equation to find the x-intercept. 15. Interpret the meaning of the x-intercept for the string problem.

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