Suppose that you calculated the mass percent of sand in the mixture to be 42%, though the original mixture really contained only 35% sand. How could you explain these results?

Answer 1

When you put the mixture together it had ro of had another compound of sand in the befinning which means that both had consentrations of sand in them

Answer 2

Another explanation is that the "dried" sand, before weighing in the last step, was not dry. The extra water was reported as sand.