1. pecahan 1/x + 1/y = 10 dan x+y= 40 . berapa xy ?

1 + 1 = 10
x    y
y+x = 10
 xy
40 = 10
xy
xy= 40
      10
xy= 4

1/x + 1/y = 10 (perkalian silang)
y+x per xy = 10
40/xy= 10
40/10 = xy
xy = 4