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UPSC Civil Service Exam Questions - Engineering

Q1:

Given that Plasticity Index (PI) of local soil = 15 and PI of sand = zero, for a desired PJ of 6, the percentage of sand in the mix should be

A 70

B 60

C 40

D 30

ANS:B - 60

Let soil and sand be in 1:x Proportion
Now,
Ip(mix)= (1*15+x*0)/(1+x)
6=(1*15+x*0)/(1+x)
x=3/2.

Now,
%of sand in the mix = (x)/(1+x) *100.
= (3/2)/(1+3/2)*100.
= 60%.