What is the frequency of this wave?

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The answer is D.

Step-by-step explanation:

It is given that Gabriella swims 2 laps for 1 minute. So in order to find how many minutes did he swim for each lap, you have to divide it by 2 :

2 laps = 1 minute

2 laps ÷ 2 = 1 minute ÷ 2

1 lap = 1/2 minute

= 30 seconds

Test :

Gabriella swim 1/2 min per lap. So if he swim 2 laps, you have to multiply it by 2 :

1/2 × 2 = 1 minute