Answer: 16 1/4 minutes
Step-by-step explanation:
Let A be the mowing rate for the first person, and B the rate for the second. X will be the time spent mowing.
We are told that A = 30 min/lawn. B = 45 min/lawn. These are conversion factors, so we can invert them to:
A = 1 lawn/30 min. B = 1 lawn/45 min
If both work together, the amount of lawn that is mowed working togehterwould be the time, X (in minutes), spent times their individual rates:
X*(A + B) = Lawn Mowed
We want to know the time, X, it would take to mow the same 1 lawn together. [Lawn Mowed = 1]. Use the equation:
X*(A + B) = Lawn Mowed
X*((1 lawn/30 min) + (1 lawn/45 min)) = 1
X/(30 min) + X/(45 min) = 1
X/30 + X/45= 1
X + X(30/35) = 30 {Multiply both sides by 30]
(1 + 30/35)X = 30
(65/35)X = 30
X = 30*(35/65)
X = 30/(7/13)
X = 30*(7/13)
X = 210/13
X = 16 1/4 minutes
