Look at the change in population in Europe from 1300 to 1400 during the black death epidemic use a calculator to determine the percentage that the population decline between those two centuries to get the answer you need to subtract the population between the two centuries then divide this difference in the population with the population in the year 1300 finally multiplied by 100 to get the decline in percentage

- "runner b is moving at a slower rate."

- "the graphs shown are graphs of distance(km) against time(min).

the slopes of this graphs are are given by:

slope = (change in y)/(change in x)

= (change in distance)/(change in time)

this is the formula for finding the speed. so, the slope of these graphs represent the speed of the runner.

taking each division in the graph to represent 1 on both axis:

runner a ⇒ speed = (2-0)/(1-0)

= 2/1

= 2 km/min

runner b ⇒ speed = (3-0)/(3-0)

= 3/3

= 1 km/min

this shows that   runner b is moving at a slower rate."