Precalculus (6th Edition) Blitzer

The number of 20th century deaths with war, famine, and tobacco is $124,111,\text{ and }71\text{ million}.$
Let us consider that the number of deaths in the 20th century due to war, famine, and tobacco is x, y, and z millions respectively. The number of deaths combing war, famine, and tobacco is 306 million; therefore the equation becomes: $x+y+z=306$ The difference between the number of deaths between war and famine is 13 million; thus we get: $x-y=13$ The difference between the number of deaths between war and tobacco is 53 million; therefore, we get: $x-z=53$ From the equation $x-y=13$, $y=x-13$ From the equation $x-z=53$, $z=x-53$ Put the value of y and z in equation $x+y+z=306$ as given below: \begin{align} & x+\left( x-13 \right)+\left( x-53 \right)=306 \\ & 3x-66=306 \\ & 3x=372 \\ & x=124 \end{align} From $y=x-13$, \begin{align} & y=124-13 \\ & =111 \end{align} From the equation $z=x-53$ \begin{align} & z=124-53 \\ & =71 \end{align} Hence, the number of deaths in the 20th century due to war, famine, and tobacco is $x=124,y=111,z=71$ million respectively.