A soil sample is subjected to laboratory sieve analysis using a complete set of standard IS sieves. Out of 3 kg of soil used in the test, 1200 gm was retained on IS 600 micron sieve, 1500 gm was retained on IS 500 micron sieve and the remaining 300 gm was retained on IS 425 micron sieve. The uniformity co-efficient for the soil is?