Math Is Fun Forum

Hi everyone, 
I really need some help. 
I am trying to slove this maths problem. It is proving really difficult. 
This is it:

Using the numbers       1, 5, 6 and 7         make 21

You are aloud to use      times, divide, plus, subtract    as meny times as you want.

You are not aloud to use the numbers more than ones and you have to use them all.

I am pretty sure that you have to go into fractions.
I just can't quite get it.
Please could you help me! 

Thanks 
from Jane