8. For both price and quantity to increase unambiguously, demand must have risen, as shown to the right. But let's be sure we understand why the other choices are incorrect.

1. An increase in the "hipness quotient" of ``sports sandals''.
2. A reduction in the cost of materials used in making the sandals would be a reduction in the cost of one of the inputs or factors of production. This would shift the supply curve out, lowering price and increasing quantity.
3. A decrease in the price of other kinds of shoes could be taken either of two ways. In the most likely case, it would be equivalent to a reduction in the price of a substitute; shifting demand back and causing price and quantity both to fall. Alternatively, it could be a reduction in the price of another product manufactured by the sandal firm; causing the supply curve for sandals to shift out, lowering price and increasing quantity.
4. An increase in the wages of shoe factory workers would be an increase in the cost of one of the inputs or factors of production. This would shift the supply curve back, raising price and reducing quantity.
5. A decrease in the wages of shoe factory workers would be a reduction in the cost of one of the inputs or factors of production. This would shift the supply curve out, lowering price and increasing quantity.