Boy scout has 3 meters of rope. he cuts the rope into cords 3/5m long. how many cords will he make

 5 pieces

Explanation:

Note how

(number of pieces)*(length per piece) = 5*(3/5) = 15/5 = 3

which is the total length of the original rope.

So that's why the answer is 5.

We can get this answer through either guess and check, or we can divide 3 over 3/5 like so

3 divide 3/5 = (3/1) divide by (3/5) = (3/1)*(5/3) = 15/3 = 5

The second fraction 3/5 flips when we divide by it. Also the division changes to a multiplication when we flip the second fraction.