1. if no digit may be used more than once, how many 5-digit numbers can be formed using only the digits 3,8,1,2,5and 7?
717 numbers
360 numbers
722 numbers
720 numbers

1. crust 1 the metallic layer at the earth's center 2. inner core 3 the firm layer between the crust and the asthenosphere 3. lower mantle 2 the layer surrounding the inner core 4. asthenosphere 4 the semi-solid layer between the top layer and the upper mantle 5. upper mantle 5 the layer between the asthenosphere and lower mantle 6. top layer 6 the earth's outermost layer 7. outer core 7 the hottest part of the mantle