Mathematics
posted by INDIANA .
A drinking straw of length 21 cm is cut into 3 pieces
the length of the first piece is x cm
the second piece is 3cm shorter than the 1st piece
the third piece is twice as long as first piece
(a) state in terms of x the length of the pieces (i think i figured that one out...1st piece= 21cmxcm, 2nd piece= xcm3cm and the 3rd piece= xcm X 2cm i don't know if its right)
(b) write an expression in terms of x to represent the sum of the lengths of 3 pieces.

You're on the right track.
I'd state it this way.
x + x  3 + 3x = 21
5x = 24
x = 24/5 = 4.8 cm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4.8 + 1.8 + 14.4 = 21 
Hmmm. I'd have said (since the 3rd piece is twice as long as the first):
x + x3 + 2x = 21
4x = 24
x = 6 
Ooops  thanks, Steve for the correction!

Hi there, you both, did not answer on the part (b)write an expression in terms of x to represent the sum of the lengths of 3 pieces.
x + (x  3) + 2x