Wire is cut into 5 equal parts. Since all dimensions are same for pieces, Resistance of each wire is equal and has a value = R/5.
Resistance is proportional to length of wire and inversely proportional to area of cross-section. IF length is 1/5th, then Resistance is also 1/5 th of original value.
When these five are connected in parallel combination, then net resistance becomes 1/5th again. So R1 = R/5 * 1/5 = R/25
Ratio = R1/R = 1/25