Transfer Game - version 2

Algebra Level pending

Two persons A A and B B have a total sum of $ 360 \$360 . First, A A gives 20 % 20\% of what he has to B B . Then B B gives 20 % 20\% of what he now has back to A A . If the final amount of each person is the same as the starting amount, what was the initial amount that person A A had?

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The answer is 200.

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2 solutions

Let initially A had $ x \$x and B had $ ( 360 x ) \$(360-x)

After A gave the money to B, he had $ 0.8 x \$0.8x and B had $ ( 360 0.8 x ) \$(360-0.8x)

After B gave money to A, the later (A) has $ ( 0.64 x + 72 ) \$(0.64x+72)

So, according to the given condition,

x = 0.64 x + 72 0.36 x = 72 x = 72 0.36 = 200 x=0.64x+72\implies 0.36x=72\implies x=\dfrac {72}{0.36}=\boxed {200} .

Chew-Seong Cheong
Sep 12, 2020

Let the initial and end amounts A A and B B have be a 0 a_0 and b 0 b_0 , and a 1 a_1 and b 1 b_1 . Then a 0 + b 0 = 360 a_0+b_0 = 360 . Then

{ b 1 = 0.8 ( 0.2 a 0 + b 0 ) = 0.16 a 0 + 0.8 b 0 a 1 = 0.8 a 0 + 0.2 ( 0.2 a 0 + b 0 ) = 0.84 a + 0.2 b 0 \begin{cases} b_1 = 0.8(0.2a_0+b_0) = 0.16 a_0 + 0.8 b_0 \\ a_1 = 0.8a_0 + 0.2(0.2a_0+b_0) = 0.84a+0.2b_0 \end{cases}

Since { b 1 = b 0 0.16 a 0 + 0.8 b 0 = b 0 b 0 = 0.8 a 0 a 1 = a 0 0.84 a + 0.2 b 0 = a 0 b 0 = 0.8 a 0 \begin{cases} b_1 = b_0 & \implies 0.16 a_0 + 0.8 b_0 = b_0 & \implies b_0 = 0.8 a_0 \\ a_1 = a_0 & \implies 0.84a+0.2b_0 = a_0 & \implies b_0 = 0.8 a_0 \end{cases}

Therefore, a 0 + b 0 = 1.8 a 0 = 360 a = 200 a_0+b_0 = 1.8 a_0 = 360 \implies a = \boxed{200}

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