Some persons can do a piece of work in 84 days. Two times the number of such persons will do half of the same work in how many days?

21 days 14 days 16 days 15 days

21 days

Formula to be used here,  ⇒ \(\frac{M_1\;×\;D_1}{M_2\;×\;D_2}\) = \(\frac{W_1}{W_2}\), where, M = No. of Men, D = No. of Days, W = Work, ⇒ Putting in the values, ⇒ \(\frac{A\;×\;84}{2A\;×\;D_2}\) = \(\frac{1}{1/2}\) ⇒ D2= 21 days,