Express as a simple fraction?

Question

If one person can water-seal a wood deck in x hours and a second person can do the same job in y hours, then the two working together can seal the deck in
h= 1 / 1/x+1/y hours,

Express h as a simple fraction

Answer 1

1/h = 1/x + 1/y (Combine the factors).
1/h = (y + x)/ xy (Spin around).
h = xy / (y + x)

Answer 2

h= 1 / 1/x+1/y

Multiply * xy/xy

h= xy /(y+x)
h= xy /(x+y)

(This is an identical formula to two resistances R1, R2 in parallel).

Answer 3

1/x + 1/y = (y + x)/xy
h = xy / (x + y) hours

Answer 4

h = xy / (x + y)

If you want to know the working, mail me at [e-mail]

Answer 5

h={1/(1/x+1/y)}
={1/(x+y)/xy}
=xy/(x+y)