Forgive the humor, but. . .what kind of sand?
See here: http://www.answers.com/Q/What_is_the_density_of_sand
And here: http://www.rfcafe.com/references/general/density-building-materials.htm
And here: http://www.engineeringtoolbox.com/density-materials-d_1652.html
The problem (which I realize you can't change) would make more sense if it was something like "how many cubic yards are taken up by 1 ton of sand with a density of 123 pounds per cubic foot?"
Below is an example using the third link's density of loose sand as 90 pounds per cubic foot. Remember that the answer depends directly on the density you start with, so the answer below doesn't answer the question "how many cubic yards does 1 ton of sand make up?" It only answers the question "how many cubic yards are taken up by 1 ton of loose sand of a particular type?"
Note: Since you're using yards (not meters), the solution below uses the standard US ton (2000 pounds), not the metric ton (1000 kilograms).
How many cubic yards are taken up by sand with a density of 90 pounds per cubic foot?
90 lbs : 1 ft^3
1 cubic yard = 3 ft * 3ft * 3ft = 27 ft^3
1 yd^3 = 27 ft^3
1/27 yd^3= 1 ft^3
90 lbs : 1/27 yd^3
But we want 1 ton, aka 2000 lbs
multiply both sides by 2000/90
90 lbs * (2000/90) : 1/27 yd^3 * (2000/90)
2000 lbs : 2000/(27*90) yd^3
2000 lbs : 2000/2430 yd^3
2000 lbs : about 0.823 yd^3
Answer: If the sand's density is 90 pounds per cubic foot, 1 ton of sand will occupy about 0.823 cubic yards.