In an office, Each and Every person likes tea or coffee, 70% of the people like tea, and 50% like coffee. Find the percentage of people who likes only tea?

50%

*If each and every person like something, then more than 100% of people like both*.

ATQ, 

Tea  + Coffee = 70% + 50% = 120%

So, Percentage of person who like both = 120% - 100% = 20%

⇒ Only tea likes = 70% - 20% = 50%