Answer: 400 wing beats
Explanation:
Find out the number of 30 second periods in 4 minutes.
If there are two 30 second periods in 1 minute, 4 minutes will have:
= 2 * 4
= 8
The swallow flaps its wings at 50 wing beats per 30 seconds. There are eight 30 seconds periods in 4 minutes .
= 50 * 8
= 400 wing beats