# It takes a man one hour to mow his lawn. It takes his son 90 minutes to mow the same lawn.?

How long will it take if father and son work together to mow the lawn?

### 9 Answers

- 8 years agoFavorite Answer
rate multiplied by time equals work done

rate of father is 1/60

rate of sone is 1/90

together (1/60 + 1/90)

to solve for time

(1/60 + 1/90)(x) = 1 (since only one mow is lawned)

hence x= 5400 / 150

or basically 36 minutes

Source(s): my math skills - FunnelwebLv 78 years ago
It will take 75 minutes because, guess what!, they only have one lawn-mower!

So the man mows half the lawn in 30 minutes, then the son mows the other half of the lawn in 45 minutes: 30 + 45 = 75 minutes.

- rhodabackLv 43 years ago
how plenty do they mow in a million hour Jack = a million/6 Marilyn = a million/3 time = x x/6 + x/3 = a million discover consumer-friendly denominator x/6 + 2x/6 = 6/6 x + 2x = 6 3x=6 divide by using 3 on the two ingredient x=2 they are going to take 2 hours to mow the backyard at the same time

- ComoLv 78 years ago
Let`s be civilised and go metric !

Let area of lawn be X m ²

father`s rate of work = X / 60 m ² / min

son`s rate of work = X / 90 m ² / min

Combined rate = X/60 + X/90 m ² / min = 5X/180 m ² / min

Time for both working together is given by :-

Area / rate = X / [ 5X/180 ] min = 180/5 min = 36 min

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- DWReadLv 78 years ago
father's speed = 1 lawn/hour

son's speed = 1 lawn/1.5 hours = 2/3 lawn/hour

combined speed = (1+2/3) lawn/hour = 5/3 lawn/hour = 3/5 hour/lawn

3/5 hour × 60 minutes/hour = 36 minutes

- Anonymous8 years ago
time=1/ ((1/60)+(1/90))

= 36 minutes

- Anonymous8 years ago
45 minutes.