Answer: Choice A
The average speed the mouse crawls is 1.5 feet every second.
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Step-by-step explanation:
1 minute = 60 seconds
The mouse crawls 90 ft in 60 seconds.
This forms the ratio
90 ft : 60 sec
Divide both parts of this ratio by 60 to get
90/60 ft : 60/60 sec
1.5 ft : 1 sec
telling us that the mouse's speed is 1.5 ft per second, which explains why choice A is the answer.