Samples of both surface soil and subsoil were taken from eight randomly selected farms in a county. The soil samples were analyzed to determine both surface pH and subsoil pH, which yielded the following results:
Farm
1 2 3 4
Surface pH: 6.55 5.98 5.59 6.17
Subsoil pH: 6.78 6.14 5.80 5.91
5 6 7 8
Surface pH: 5.92 6.18 6.43 5.68
Subsoil pH: 6.10 6.01 6.18 5.88
a. Compute a 90% confidence interval for the true average difference between surface and subsoil pH for farmland in this county.
b. What assumptions are necessary to validate the interval in Part a?
Please help with any info./formula/calculator notation... Anything!
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