Question 121685
19. Let's call the angles A1, A2, A3. 
1.{{{A2=2*A1}}}
2.{{{A3=A2+10=2*A1+10}}}
From your triangle knowledge you also know that the sum of the angles of a triangle equals 180 degrees.
3.{{{A1+A2+A3=180}}}

Now substitute your values from equation 1 and 2 into equation 3.
3.{{{A1+A2+A3=180}}}
{{{A1+(2*A1)+(2*A1+10)=180}}}
{{{5*A1+10=180}}}
{{{5*A1=170}}}
{{{highlight(A1=34)}}}
From 1,
1.{{{A2=2*A1}}}
{{{A2=2*34}}}
{{{highlight(A2=68)}}}
From 2,
2.{{{A3=A2+10}}}
{{{A3=68+10}}}
{{{highlight(A3=78)}}}
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.
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20. The perimeter of a rectangular writing pad is 28 inches. The length is 1 inch less than twice the width. Find the width. 
1.{{{P=2W+2L=28}}}
2.{{{L=2W-1}}}
Substitute 2 into 1 and solve for W.
1.{{{2W+2L=28}}}
{{{2W+2(2W-1)=28}}}
{{{2W+4W-2=28}}}
{{{6W-2=28}}}
{{{6W=30}}}
{{{highlight(W=5)}}}
From 2,
2.{{{L=2W-1}}}
{{{L=2(5)-1}}}
{{{L=10-1}}}
{{{highlight(L=9)}}}