Kei got the best deal.
Explanation
The ratio of cost to number of books purchased for all of four friends will be.....
Jo ⇒ [tex]\frac{9}{4}[/tex] , Kei ⇒ [tex]\frac{12}{8}[/tex] , Kate ⇒ [tex]\frac{30}{16}[/tex] , Bryn ⇒ [tex]\frac{8}{4}[/tex]
Now we need to find the fraction which has lowest value. So, first we will make the denominators of all fractions as equal and then identify the lowest numerator. So......
[tex]\frac{9}{4}=\frac{9*4}{4*4}=\frac{36}{16}\\ \\ \frac{12}{8}=\frac{12*2}{8*2}=\frac{24}{16}\\ \\ \frac{30}{16}=\frac{30*1}{16*1}=\frac{30}{16}\\ \\ \frac{8}{4}=\frac{8*4}{4*4}=\frac{32}{16}[/tex]
We can see that, the lowest numerator is 24 here. That means the lowest fraction is [tex]\frac{12}{8}[/tex]
Thus, Kei got the best deal.
