P(atleast 1 tail ) =  1 - P( no tail )

= 1−(1/2)*4=15/16

Explanation -
Total Occurrences = 2*2*2*2 = 16.

Probability of getting only heads is 1/16 so automatically probability of getting tails in 4 tosses of a coin becomes 15/16.

Practice more problems from this chapter as this is a chapter from where the questions are sure short asked in the entrance exams like MHT CET OR JEE MAINS.

BEST WISHES. THANKYOU.