1)A jetskier is moving at 8.2 m/s in the direction in which the waves on a lake are moving. Each time he passes over a crest, he feels a bump. The bumping frequency is 1.05 Hz, and the crests are separated by 5.8 m. What is the wave speed?
so here I used speed = frequency x wavelength, for frequency 1.05 Hz and wavelength 5.8 m and got 6.09 m/s, the computer said that was wrong so I tried doubling the frequency(thinking that if they only counted the upper crests id need to include the troughs), then got 12.20 m/s which was also wrong.

2)The mass of a string is 5.3 × 10-3 kg, and it is stretched so that the tension in it is 150 N. A transverse wave traveling on this string has a frequency of 290 Hz and a wavelength of 0.53 m. What is the length of the string?
Here I used speed= square root of ( tension/mass/length), I calculated speed first by speed = frequency 290 x wavelength .53 got 153.7, plugged that in and got 184.14 m as the string length which the computer said was wrong.

Can anyone see where I've gone wrong? I've tried messing around with the sig figures but maybe that's my error? Thanks