A group of swimmers is resting in the sun on an off-shore raft. They estimate that 2.5 m separates a trough and an adjacent crest of surface waves on the lake. They count 15 crests that pass by the raft in 15 s. How fast are the waves moving?

____m/s

(I got these answers and none of them were correct)
.17
6.07
6.05
5.56
4.86
4.9
5.6
4.85

2 answers

frequency*wavelength=speed
15/15 * 2*2.5=speed
I am wondering how you got any of those answers?
I have no idea. I'm pretty sure I used 2.6 instead of 2.5 on accident! OOPS