Question

10% of salty sea water contained in a flask was poured out in a beaker

Answer 1

Original % of salt in the flask = A
let 100 ml solution is there. 
10 % of this is taken out ,it will have A/10 gm salt.
But by evaporation this becomes = A/10' 
This salt is added back to the flask so total salt in the flask now
= 0.9A +A/10'

actual rise in salinity= x%
so total salt will be =0.9(A+x) 

=0.9A+ A/10'
= 0.9(A+x)