Stickers are sold in packages of 15 sheets. If there are 20 students in the class, how many packages of stickers should the teacher buy so that every student gets the same amount of sheets, with none left over?

4

Step-by-step explanation:

because 15 x 4 = 60

20 x 3 = 60

large crystals result from very slow cooling.

evaporation of water: this would produce an evaporite which is a sedimentary rock. like a salt pan in a desert. not possible to have volcanic rocks originate this way.

crystalization in molten earth: slow cooling over time. (hundreds to millions of years)

crystalization at earth's surface: this results in fast cooling. (a few hours to a few months or years)

crystalization from cooling off hot water: that would be a hydrothermal deposit. while associated with volcanics they are not volcanic rocks themselves and usually occur fairly rapidly.