can you help me with math I don't understand that.

Question

Stan and Hilda can mow the lawn in 20 min if they work together. If Hilda works twice as fast as Stan, how long does it take Stan to mow the lawn alone?

Answer 1

Let x = time (in minutes) that it takes Hilda to mow the lawn by herself

 

Then 2x = time (in minutes) that it takes Stan to mow the lawn by himself

 

1/x = portion of the lawn mowed by Hilda in one minute

 

1/(2x) = portion of the lawn mowed by Stan in one minute

 

So, 1/x + 1/(2x) = 1/20

 

Multiply through by the LCD, 20x, to obtain 20 + 10 = x.

 

                                                                         x = 30 min

 

Stan's time = 2x = 60 min 

Answer 2

H+S=1/20 amount of job they do each minute

H=1/2S Since Hilda mows twice as fast as Stan, it takes half time as much as Stan needs to mow

 

So, it takes 30 minutes to Stan to mow the lawn alone.

Note: H stands for Hilda, and S stands for Stan.