Answer: The fraction would be 0.53.
Step-by-step explanation:
Since we have given that
[tex]r(t)=A.(1.05)^t[/tex]
where, A is the constant initial production rate
t is the time.
For 98 years, the production rate in motorcycles per year would be
[tex]r(98)=A.(1.05)^{98}\\\\r(98)=A.119.27[/tex]
For 13 years, the production rate in motorcycles per year would be
[tex]r(98-13)=r(85)=A.(1.05)^{85}\\\\r(85)=A.63.25[/tex]
So, the fraction of their total production was built during the last 13 years would be
[tex]\dfrac{r(85)}{r(98)}=\dfrac{63.25}{119.27}=0.53[/tex]
Hence, the fraction would be 0.53.