A man, a woman and a boy can complete a work in 3, 4 and 12 days, respectively. How many must assist one man and one woman to complete the same work in one day?

5

Man = 3 days, Woman = 4 days, Boy = 12 days,

Let's take extra people needed as x.

⇒ \(\frac{Total Work}{Total efficiency}\) = Time

⇒ \(\frac{12}{(4 + 3) + x}\) = 1 

⇒ 12 = 7 + x 

⇒ x = 12 - 7 = 5

Therefore, 5 people are needed to assist one man and one woman to complete the same work in 1 one day.