Answer:
1.9393 hours
Step-by-step explanation:
In general, if the learning curve is p%, then the time [tex]\bf T_n[/tex] estimated to produce the nth unit is given by the logarithmic curve
[tex]\bf T_n=T_1n^b[/tex]
where
[tex]\bf T_1[/tex] is the time needed to produce unit 1
and b is given by
[tex]\bf b=\frac{log(p/100)}{log(2)}[/tex] (slope of the learning curve)
In our case
[tex]\bf T_n=T_1n^{log(0.85)/log(2)}=T_1n^{(-0.2344)}[/tex]
So we must find [tex]\bf T_1[/tex]
We know that the cumulative average labor hours to assemble the first five units of product A was 15.962 hours, hence
[tex]\bf T_1+T_2+T_3+T_4+T_5=15.962[/tex]
applying the formula,
[tex]\bf T_1+T_12^{(-0.2344)}+T_13^{(-0.2344)}+T_14^{(-0.2344)}+T_15^{(-0.2344)}=15.962[/tex]
factorizing
[tex]\bf T_1(1+2^{(-0.2344)}+3^{(-0.2344)}+4^{(-0.2344)}+5^{(-0.2344)})=15.962[/tex]
computing the terms we have
[tex]\bf T_1(4.0311)=15.962\rightarrow T_1=3.9597\;hours[/tex]
Finally, to compute the time estimated to produce the 21st unit, we replace in the formula with n=21
[tex]\bf \boxed{T_{21}=3.9597(21)^{-0.2344}=1.9393\;hours}[/tex]