The boy, the sneakers and the whistles
Note that we are working with three variables (boy, tennis and whistle).
In the first equation, calling the pair of sneakers xwe have:
x + x + x = 30
3x = 30
x = 10 (so a pair of sneakers is worth 10)
In the second equation, most people make mistakes, so pay attention:
Note that in the second equation the boy has a whistle around his neck. Calling this boy with the whistle around his neck ywe have:
10 + y + y = 20
2y = 20-10
y = 10/2
y = 5 (so the boy with the whistle around his neck is worth 5)
In the third equation, note that in the last two terms there are 2 whistles in each. So calling the whistle of zwe have:
5 + 2z + 2z = 13
4z = 13-5
4z = 8
z = 2 (so the whistle is worth 2)
Finally, in the last equation, see that we have two operations: an addition and a multiplication (which must be done before the addition). Also note that the first term shows only one foot of the shoe (thus, the value of the pair of shoes must be divided by 2), while the second term shows a boy without the whistle around his neck (thus, we must subtract from him the value of the whistle which is 2). Performing the operations, we have:
(10/2) + (5-2) x 2 =?
5 + (3x2) =?
5 + 6 = 11
Thus, the result of the last equation is 11.
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