Which sequence is geometric and has 1/4 as its fifth term and 1/2 as the common ratio?

5th term = a1r^4 where a1 = first term and r = common ratio

so 1/4 = a1 * (1/2) ^4

a1 = 1/4 / (1/2) ^4 = 4

so the sequence is 4, 4*1/2, 4 * (1/2) ^2 ...

= 4, 2, 1, 1/2, 1/4 ...