Question

the velocity of sound in air 27 C is 340m/s calculate velocity of sound in air at 127 C

Answer 1

340 m/s * sqrt(400/300) = 392.6 m/s

The velocity of sound is proportional to the square root of the absolute temperature, if the molecular weight of the gas stays the same.

Answer 2

I have also assumed that the "gamma" (specific heat ratio Cp/Cv) is the same for air at both temperatures (27 and 127 C). This is a valid assumption up to about 200 C.
http://www.engineeringtoolbox.com/specific-heat-ratio-d_602.html

speed of sound = sqrt(gamma*R*T/M)
M = molecular weight = 28.97 for air
gamma = specific heat ratio = 1.40 for air
T = absolute temperature
R = gas constant per mole

Answer 3

392.6 m/s

Answer 4

wrong question