One has a frequency of 490 Hz and the other is 488 Hz. How many beats per second are heard?

When sounds at two different frequencies are combined,

two new sounds are created ... at the sum and difference

of the original frequencies.

Combining two sounds at 490 Hz and 488 Hz creates

beats at 978 Hz and 2 Hz.

The fluttering "wah wah" effect of the 2 Hz beat is much more

noticeable than the new sound at 978 Hz.