Final answer:
To find the new mean height after adding an eighth pony with a height of 128 cm to seven ponies with a mean height of 116 cm, calculate the total height of all ponies and then divide by the number of ponies, resulting in a mean height of 117.5 cm.
Step-by-step explanation:
The subject of this question is Mathematics and it targets students at a High School level. To calculate the new mean height after Pete buys an eighth pony, you need to follow these steps:
First, calculate the total height of the initial seven ponies by multiplying the mean height by the number of ponies (116 cm x 7 = 812 cm).
Add the height of the eighth pony to this total (812 cm + 128 cm = 940 cm).
Divide the new total height by the number of ponies to find the new mean height (940 cm / 8 ponies = 117.5 cm).
The mean height of all eight ponies is 117.5 cm.