Distributing coins trouble

Algebra Level 2

There are four persons A , B , C , D A,B,C,D and A A has some coins.

A A gave half of the coins to B B and another 4 more coins.
B B gave half of the coins to C C and another 4 more coins.
C C gave half of the coins to D D and another 4 more coins.
Both B B and D D end up with same number of coins.

How many coins did A A have originally?


The answer is 72.

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1 solution

Let the coins A A originally had be N N . Then, we have:

N { A : N 2 4 B : N 2 + 4 { B : N 4 2 C : N 4 + 6 { C : N 8 1 D : N 8 + 7 N \Rightarrow \begin{cases} A: \dfrac {N}{2} - 4 \\ B: \dfrac {N}{2} + 4 \Rightarrow \begin{cases} B: \dfrac {N}{4} - 2 \\ C: \dfrac {N}{4} + 6 \Rightarrow \begin{cases} C: \dfrac {N}{8} - 1 \\ D: \dfrac {N}{8} + 7 \end{cases} \end{cases} \end{cases}

B B got N 4 2 \dfrac {N}{4} - 2 and D D got N 8 + 7 \dfrac {N}{8} + 7

N 4 2 = N 8 + 7 N 8 = 9 N = 72 \begin{aligned} \Rightarrow \dfrac {N}{4} - 2 & = \dfrac {N}{8} + 7 \\ \dfrac {N}{8} & = 9 \\ \Rightarrow N & = \boxed{72} \end{aligned}

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