The only three single digit odd prime numbers are 3, 5 and 7. So the length of the first piece = (3+ 5 + 7)/3 = 5. Now let the length of the second piece = Y units.

Then by the condition given in question we have – Length of the third piece = Y + 5. Length of the second piece = Y = 5 + (Y + 5)/3.

Solve this to get Y = 10. So, length of the first piece = 5, second piece = 10 and third piece = 15. So length of the original sheet = 5 + 10 + 15 = 30 units.