Question 123283
Julio needs to draw a line 15 cm long. He does not have a ruler. He does have several sheets of paper that measure 28.0 cm by 21.5 cm. How can he use these papers to draw his 15 cm line?

<pre>
Lay two sheets sideways, one above the other,
with their 28cm sides together, like this:

{{{drawing(200,175,-5,50,-5,50,
rectangle(0,0,28,21.5), 
rectangle(0,21.5,28,43),
locate(-3,45,A), locate(-3,-1,B),
locate(29,11,21.5),locate(29,32.5,21.5),
locate(12,-1,"28.0"),locate(12,48,"28.0")

)}}}

This makes a rectangle which is 2x21.5cm 
or 43cm tall. So AB = 43cm.

Now place a third sheet upright on top of those
like this:

{{{drawing(200,175,-5,50,-5,50,
rectangle(0,0,28,21.5), 
rectangle(0,21.5,28,43),
rectangle(0,0,21.5,28),
locate(29,11,21.5),locate(29,32.5,21.5),locate(12,48,"28.0"),
locate(-3,45,A), locate(-3,-1,B), locate(-3,29,C)
)}}}

Now since AB = 43cm, and BC = 28cm,
then AC = AB - BC = 43cm - 28cm = 15cm.

Edwin</pre>