Correct Answer - Option 1 : 21 days
Given:
Time taken by 12 machines working 7 hours a day = 18 days
Formula used:
(M1 × D1 × H1)/W1 = (M2 × D2 × H2)/W2
Calculation:
By using the above formula for calculating the no of days:
(12 × 18 × 7)/1 = (16 × D2 × 9)/2
⇒ 12 × 18 × 7 × 2/(16 × 9) = D2
⇒ D2 = 21 days
∴ 16 machines working 9 hours a day finish twice the work in 21 days.