Equal masses of three liquids, A, B and C have temperatures $ 10^{\circ}C, 25^{\circ}C \: and \: 40^{\circ}C$ respectively. If A and B are mixed, the mixtures has a temperature of $15^{\circ}C$. If B and C are mixed, the mixtures has a temperature of $30^{\circ}C$. If A and C are mixed, the temperature of the mixture is

Question

$\begin {array} {1 1} (1)\;35^{\circ}C & \quad (2)\;25^{\circ}C \\ (3)\;20^{\circ}C & \quad (4)\;16^{\circ}C \end {array}$