When the price of pencils increases from $1.50 to $2.50, there is an increase in quantity demanded of pens from 100 to 150. the cross-price elasticity of demand between pencils and pens is: ?

explanation:

a gas is not used in hydraulic machines as the fluid because gas is easily compressible and so if a gas is used, the energy would mostly go into compressing a gas. therefore a liquid is used in hydraulic machines as the fluid.

the page presents four different kinds of threats that volcanoes pose and what to do before, during, and after an eruption.

answer (b); /// a method of measuring the opinions of a large group of people by selecting a subset of the larger group, asking them a set of questions and then generalizing those responses;