On sixth of February, Sudhir tells his aunt , “I went for a picnic with my classmates exactly 15 days ago.” When was his picnic?

a) 22nd January b) 28th February c) 21stJanuary d) 21stFebruary

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.