Question 1114109
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Ben and Greg go to the movies and purchase snacks. Ben purchases four cookies and two bottles of water for a total cost of $9.00. 
Greg purchases two cookies and two bottles of water for a total cost of $7.00. What is the cost of a bottle of water?


<pre>
    Good style in solving such problems is to notice/(to observe) immediately from the condition that the difference 
    between two combinations is  the cost of 2 cookies,  and it is equal to  $9 - $7 = $2.   So  2 cookies cost  $2.


    Then subtracting $2 dollars for 2 cookies from the Greg purchase, you got the cost of two bottles - it is equal to  $7 - $2 = $5. 


    <U>Answer</U>.  A bottle of water costs  $2.50.
</pre>


This problem is for mental solution,  and it would be ideally if you see the solution immediately/instantly as you completed reading its condition. 



There is no any need to write and to solve a system of equations.


See the lesson

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/coordinate/lessons/Solving-mentally-word-problems-on-two-equations-in-two-unknowns-NEW.lesson>Solving mentally word problems on two equations in two unknowns</A> 

in this site.


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Such problems are good for using in interviews, &nbsp;if the employer want to check whether the interviewed  had special training in Math.


If your solution follows my scheme, &nbsp;the interviewer marks &nbsp;"YES"&nbsp; in his check-list.


If you follow the @josgarithmetic way, &nbsp;the interviewer marks "NO" in the check-list.


In the second case, &nbsp;the interviewed person even doesn't know and doesn't understand for what reason the question/(the problem) was given to him.