Answer
$x̅=70.6~°F$
$s=3.5~°F$
Work Step by Step
$x_1=$ First Class Midpoint = 63
$x_2=$ Second Class Midpoint = 66.5
$x_3=$ Third Class Midpoint = 69
$x_4=70$
$x_5=$ Fifth Class Midpoint = 72
$x_6=$ Sixth Class Midpoint = 75
$x_7=$ Seventh Class Midpoint = 79
$x̅=\frac{Σx_if_i}{Σf_i}=\frac{63\times31+66.5\times67+69\times198+70\times195+72\times120+75\times89+79\times50}{750}=70.6$
$s=\sqrt {\frac{Σ(x_i-x̅)^2f_i}{(Σf_i)-1}}=\sqrt {\frac{(63-70.65)^2\times31+(66.5-70.65)^2\times67+(69-70.65)^2\times198+(70-70.65)^2\times195+(72-70.65)^2\times120+(75-70.65)^2\times89+(79-70.65)^2\times50}{750-1}}=3.5$
