if I climb with my mother on a scale I weighed 103kg, and if I get on with my father, 113kg. If my father and mother together weigh 126kg, how many kilos do the three of us weigh all together?
A)168 B)169 C)170 D)171 E)172
\(\small{ \begin{array}{lrcll} (1) & i + \text{ mother } &=& 103\ \text{kg} \\ (2) & i + \text{ father } &=& 113\ \text{kg} \\ (3) & \text{ father }+\text{ mother } &=& 126\ \text{kg} \\ \hline (1)+(2)+(3) & (i + \text{ mother }) + (i+ \text{ father }) + (\text{ father }+\text{ mother }) &=& 103\ \text{kg} + 113\ \text{kg} + 126\ \text{kg}\\ & 2\cdot i + 2\cdot \text{ mother } + 2\cdot \text{ father } &=& 103\ \text{kg} + 113\ \text{kg} + 126\ \text{kg}\\ & 2\cdot i + 2\cdot \text{ mother } + 2\cdot \text{ father } &=& 342\ \text{kg}\\ & 2\cdot( i + \text{ mother } + \text{ father } ) &=& 342\ \text{kg}\\ & i + \text{ mother } + \text{ father } &=& \frac{ 342 } { 2 } \ \text{kg}\\ & \mathbf{ i + \text{ mother } + \text{ father } }& \mathbf{=} & \mathbf{ 171\ \text{kg} }\\ \end{array} }\)
The three of us weight all together 171 kg
The answer is D)
