Well each fraction should add up to be one.
To do this you need the LCD for 5, 6, 3, and 4.
The LCD is 60.
2/5, multiply by 12/12 and get: 24/60
1/6, multiply by 10/10and get:
10/60
1/3, multiply by 20/20 and get:
20/60
1/4, multiply by 15/15 and get:
15/60
Add 24/60+10/60+20/60+15/60. You get 69/60 which is not equal to 1. So that is why it is not true.