Interactive practice questions
Select the graph that shows a negative relationship between the two variables.
In a laboratory experiment, a scientist measures the time $T$T (in seconds) that it takes for a chemical reaction to finish, after adding acids of different strengths $P$P (measured as pH). The pH scale, which is used to measure the strength of an acid, allows values from $-7$−7 (a strong acid) to $+7$+7 (a very strong base).
The least-squares equation for the given data is $T=-10P+140$T=−10P+140.
Soil salinity is a problem that affects large areas of farmland in Australia. A farmer has measured wheat production $W$W (in tonnes per hectare) for a number of paddocks with various salt levels $S$S (in kg per hectare).
The least-squares equation for the given data is approximately $W=-\frac{3}{5}S+300$W=−35S+300.
The fleet manager for the Australian Automotive Association wants to estimate how car maintenance costs $C$C (in hundreds of dollars) are related to the distance $K$K (in thousands of kilometres) driven each year.
The data collected is shown in the scatter plot below and the least-squares equation $C=9.9K+146.2$C=9.9K+146.2.