Scientists improved Mendeleev’s early periodic table by . using numbers of neutrons and protons to organize the elements by their properties

using atomic number instead of atomic mass to organize the elements

including physical properties of elements such as melting point and density

including chemical properties of elements such as the ability to burn or to tarnish

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?