What is a counting system? what different types of counting systems are there? please help !

A numeral system is a writing system for expressing numbers; that is, a mathematical notation for representing numbers of a given set, using digits or other symbols in a consistent manner. The same sequence of symbols may represent different numbers in different numeral systems.

Step-by-step explanation:

Different types:

Oksapmin, base-27 body part counting. Photo Courtesy of Austronesian Counting. ...

Tzotzil, base-20 body part counting. ...

Yoruba, base-20 with subtraction. ...

Traditional Welsh, base-20 with a pivot at 15. ...

Alamblak, numbers built from 1, 2, 5, and 20. ...

Ndom, base-6. ...

Huli, base-15. ...

Bukiyip, base-3 and base-4 together.

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.

- "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."