The greatest length of the scale that can measure exactly 20 cm, 90 cm, 1 m 25 cm and 1 m 30 cm length is:

5 cm 

20 cm, 90 cm, 1 m 25 cm and 1 m 30 cm 

20 cm, 90 cm, 125 cm, 130 cm

To measure the above lengths exactly, we need HCF of above numbers.

HCF of 20, 90, 125, 130 is = 5

Therefore, 5cm is the greatest length of the scale that can measure exactly 20 cm, 90 cm, 1 m 25 cm and 1 m 30 cm lengths.