let [tex]a_n[/tex] represent the number of bacteria after [tex] \frac{n}{2} [/tex] hours.
so
[tex]a_0[/tex] is the number of bacteria after 0/2 = 0 hours
[tex]a_1[/tex] is the number of bacteria after 1/2 hours
[tex]a_2[/tex] is the number of bacteria after 2/2 = 1 hours and so on
so if we list a few terms of this sequence, we have:
[tex]a_0=1[/tex]
[tex]a_1=1*2[/tex]
[tex]a_2=1*2*2[/tex]
[tex]a_3=1*2*2*2[/tex]
[tex]a_4=1*2*2*2*2[/tex]
so clearly, [tex]a_n[/tex], the number of bacteria after [tex] \frac{n}{2} [/tex] hours, is equal to [tex] 2^{n} [/tex].
[tex]a_4_8[/tex] is the number of bacteria after
[tex]\frac{n}{2}=\frac{48}{2}= 24[/tex] hours.
Thus, we calculate [tex]a_4_8[/tex], which is [tex] 2^{48} [/tex].
Answer: the number of bacteria after 24 hours is [tex] 2^{48} [/tex].