Ihave to estimate the product of 0.67 x 623 using compatible numbers..

possible answers:
about 420
about 280
about 42
about 36

i tried it and i didn't do very well, i don't really feel like doing it myself so an answer would be appreciated, .

Answer this question! 30 points and brainliest! only if you know the answer.

If the speed of an electromagnetic wave is 100,000 cm/s and its wavelength is 100 cm, what is its frequency? a) 100,000 cycles per second (hz) b) 1 × 10-3 cycles per second (hz) c) 10,000,000 cycles per second (hz) d) 1,000 cycles per second (hz)

Miguel’s teacher asks him to color 4/8 of his grid. he must use 3 colors: red, blue, and green. there must be more green sections than red sections. how can miguel color all the sections of his grid to follow all the rules