The sample mean is X[bar]=$1500
The sample standard deviation is S=$100
The sample size is n=70
The data set has a bell shaped distribution
The empirical rule states that
The values $1400 and $1600 are within one standard deviation away from the mean:
X[bar]+S=$1500+$100=$1600
X[bar]-S=$1500-$100=$1400
Following the rule you can expect 68% of the sample to be between them.
Whats left to do is to calculate the 68% of the sample
[tex]70\cdot0.68=47.6[/tex]Around 47.6 of the farms have values per acre are between $1400 and $1600