Question 1205950
<pre>
Henry had a pole measuring 7 m. He painted it red, yellow and black. 

(1)  {{{R + Y + B = 7}}}

He painted 1 3/4 of the pole red. 

{{{1&3/4*7 = R}}}
(2)  {{{7/4 = R}}}

The length of the black part was 3/4 of the length of the yellow part. 

(3) {{{B=expr(3/4)*Y}}}

What was the length of the pole that was {{{cross(poured)}}} painted black?

Substitute (2) and (3) in (1)

{{{R + Y + B = 7}}} 

{{{7/4+Y+expr(3/4)*Y=7}}}

Multiply through by 4

{{{7+4Y+3Y=28}}}

{{{7Y=21}}}

{{{Y=3}}}

Substitute in (3)

{{{B=expr(3/4)*expr(3)}}}

{{{B = 9/4}}}

{{{B = 2.25}}} meters

Edwin</pre>