Getting a piano into a truck isn't easy, so we often use a ramp to lower the amount of required force. Three students want to use least effort to put the piano into a truck. They have tried ramps with different length- 3 m, 4 m and 5 m. They have observed that the three of them are needed when the length is 3 m, two of them when the ramp is 4 m and just one when the ramp is 5 m.

they should use 5m ramp as it requires the least effort from the student.

Best answer that i found on yahoo ok   set :   x= length of 2nd piece in cm  x- 3= length of 1st piece in cm  x-4= length of 3rd piece in cm  then since you know they all came from the 20 cm ribbon you add them together and set them equal to 20x+ x-3 +x-4 = 20  3x - 7= 20  3x= 27  x= 9  the shortest piece is the third piece which is x- 4  x-4  9-4 = 5  the length of the smallest piece is 5 cm.  the other lengths are  9 cm  6 cm