Group index, GI = 0.2a + 0.005ac + 0.01bd
a = % passing 75 µm sieve greater than 35 but not exceeding 75 (expressed as a whole number from 0 to 40)
b = % passing 75 µm sieve greater than 15 and not exceeding 55 (expressed as a whole number from 0 to 40)
c = liquid limit in excess of 40 and less than 60 (expressed as a whole number from 0 to 20)

d = plasitcity index exceeding 10 and not more than 30 (expressed as a whole number from 0 to 20)
Here, a = (62 – 35) = 27

b = (62 – 15) = 27
b = (62 – 15) = 47 (Range 0-40)
Adopt, b = 40
c = (WL – 40) < 0 (as the value comes negative) 
Adopt, c = 0

d = (IP – 10) = (14 – 10) = 4