Correct Answer is: (a) 16°C
θ = Σmsθ/Σms = m1s1θ1 + m2s2θ2 + / m1s1 + m2s2 +
For systems of equal mass, θ = Σmsθ/Σs
Let s1, s2 and s3 be the specific heat capacities of A, B and C respectively.
For A + B, 15 = 10s1 + 25s2/s1 + s2
or 5s1 = 10s2
or s1 = 2s2
For B + C, 30 = 25s2 + 40s3/s2 + s3
or 5s2 = 10s3
or s3 = 0.5s2.
For A + C, θ = 10s1 + 40s3/s1 + s3 = 10(2s2) + 40(0.5)s2/2s2 +0.5s2 = 40/2.5 =16.