A man weighs 100 kilograms plus half its own mass. What is his total mass?

$${\mathtt{M}} = {\mathtt{100}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{M}}}{{\mathtt{2}}}}$$

$${\mathtt{M}}{\mathtt{\,-\,}}{\frac{{\mathtt{M}}}{{\mathtt{2}}}} = {\mathtt{100}}$$

$${\frac{{\mathtt{2}}{M}}{{\mathtt{2}}}}{\mathtt{\,-\,}}{\frac{{\mathtt{M}}}{{\mathtt{2}}}} = {\mathtt{100}}$$

$${\frac{{\mathtt{M}}}{{\mathtt{2}}}} = {\mathtt{100}}$$

$${\mathtt{M}} = {\mathtt{200}}$$

Let M be the mass. Then

M = 100 + M/2

Subtract M/2 from both sides

M/2 = 100

Multiply both sides by 2

M = 200 kg  (Heavy man!)

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