One morning after waking up from sleep, 2/3 learned that one of its forms “slash 15” (/15) had lost their head! 2/3 was deeply upset because /15 was in such a state.

So 2/3 jumped out of bed, put on its 4/6's costume and headed to the Lost Head & Found Department (LHFD) at City Hall. There 4/6 saw so many fraction heads that it became very upset.

“I wish I could help them all find their heads,” fretted 4/6. “But right now it's /15’s head that I want to find especially since /15 is a clone of mine.”

“Could you help me?” pleaded 4/6.

1/5, the head of LHFD, heard 4/6’s plea and came to the rescue.

“Let's see now,” ponders 1/5. “What could /15 be and still be 4/6?”

In other words (or rather numbers):
 
“One way to find out is to list all of your clone members,” 1/5 informed 4/6.

“OK, I’ll do that,” replied 4/6. “Let's see,” said 4/6, “my clone costumes are 2/3, 6/9, 8/12, 10/15...”

“That's it,” interrupted 1/5, "10 is /15's head!”
 
“You got it,” agreed 4/6. “Some of my other clone members are 12/18 and 14/21,” continued 4/6.