A signal with 200 milliwatts power passes through 10 devices, each with an average noise of 2 microwatts. what is the snrdb

Given that the signal is 200 mW, you will convert this into Wats;

200/1000 = 0.2W

Noise = 10*2*10⁻⁶=2*10⁻⁵

Therefore the SNR = Average signal power:Average noise power

0.2/2*10⁻⁵=10000

Thus:

SNR db = 10 ㏒₁₀ (SNR)

So in this case 10 ㏒₁₀ (10000) = 40.