Question

a 240 centimeter board is to be cut into two pieces so that the longer piece is twice as long as the shorter piece. find the length of each piece.

Answer 1

You need two pieces and 1 has to be 2x longer than the other 
set x as the smaller piece (easier to always go with the smaller value as x)
the other piece is 2x (double in size)
your equations would be 3x=240>>> x= 60

so smaller piece/ x= 60
bigger piece/ 2x= 120

Answer 2

If the side lengths are 240, then the answer is one length is 240 and one length is 120 cm