How many Eggs??

Algebra Level 2

A man was carrying some eggs with him. He sold 1 2 \frac{1}{2} of all the eggs he had and 1 2 \frac{1}{2} of an egg to a customer. He sold 1 2 \frac{1}{2} of the remaining eggs he had and 1 2 \frac{1}{2} of another egg to another customer. To the third customer, he sold 1 2 \frac{1}{2} of the remaining eggs and 1 2 \frac{1}{2} of an egg. All of his eggs had been sold to the 3 customers. How many eggs did he originally have if he hadn't broken any eggs?


The answer is 7.

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3 solutions

Let the original number of eggs be n n .

  • To the first customer he sold n 2 + 1 2 \dfrac n2 + \dfrac 12 and number of eggs remained was n n 2 1 2 = n 2 1 2 n - \dfrac n2 - \dfrac 12 = \dfrac n2 - \dfrac 12 .
  • To the second customer he sold 1 2 ( n 2 1 2 ) + 1 2 \dfrac 12 \left(\dfrac n2 - \dfrac 12\right) + \dfrac 12 and number of eggs remained was n 2 1 2 1 2 ( n 2 1 2 ) 1 2 = n 4 3 4 \dfrac n2 - \dfrac 12 - \dfrac 12 \left(\dfrac n2 - \dfrac 12\right) - \dfrac 12 = \dfrac n4 - \dfrac 34 .
  • To the third customer he sold 1 2 ( n 4 3 4 ) + 1 2 \dfrac 12 \left(\dfrac n4 - \dfrac 34\right) + \dfrac 12 and number of eggs remained was 0 0 .

Then, we have:

n = n 2 + 1 2 + 1 2 ( n 2 1 2 ) + 1 2 + 1 2 ( n 4 3 4 ) + 1 2 Multiply both sides by 8. 8 n = 4 n + 4 + 2 n 2 + 4 + n 3 + 4 n = 7 \begin{aligned} n & = \frac n2 + \frac 12 + \frac 12 \left(\frac n2 - \frac 12\right) + \frac 12 + \frac 12 \left(\frac n4 - \frac 34\right) + \frac 12 & \small \blue {\text{Multiply both sides by 8.}} \\ 8n & = 4n+4 + 2n - 2 + 4 + n - 3 + 4 \\ \implies n & = \boxed 7 \end{aligned}

Richard Desper
Nov 15, 2019

Going backwards: if z z is the number of eggs the man had before he sold eggs to the third customer, then z = z / 2 + 1 / 2 z = z/2 + 1/2 . Thus z = 1 z = 1 .

If y y is the number of eggs the man had before he sold eggs to the second customer, then y = y / 2 + 1 / 2 + 1 y = y/2 + 1/2 + 1 . Thus y = 3 y = 3 .

If x x is the number of eggs the man had before he sold eggs to the first customer, then x = x / 2 + 1 / 2 + 3 x = x/2 + 1/2 + 3 . Thus x = 7 x = 7 .

p.s. It was unnecessary to mention that the man had not broken any eggs. The values of x , y x,y , and z z are integral from the algebra. There is no non-integer solution to this system.

Solving the equation x = x 2 + 1 2 + x 1 4 + 1 2 + x 3 8 + 1 2 x=\dfrac{x}{2}+\dfrac{1}{2}+\dfrac{x-1}{4}+\dfrac{1}{2}+\dfrac{x-3}{8}+\dfrac{1}{2} for x x we get the answer as x = 7 x=7

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