You can probably solve this one in your head. For my explanation, highlight the space between the [brackets] below.
[EXPLANATION: (Did I put this one up before? I don't remember.) As you see at the outset, five stacked glasses have a total height of 29 cm. Two glasses have a height of 17. The glasses fit into each other, so the five stacked glasses equal one whole glass (x) plus four exposed parts (4y). So x + 4y = 29. For the two stacked glasses, x + y = 17. The question, then, is: What is x? Let's set up a system of equations:
x + 4y = 29
x + y + 17
Subtract the second equation from the first, and the result is:
3y = 12, so y = 4.
So if x + y = 17, then substitute a 4 for y, and x + 4 = 17, so x = 13. QED.
The Math Queen also offers a visual way to solve the problem.]
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