Question 312343
Rate*Time=Distance
{{{W}}}-wind speed
{{{P}}}-plane speed
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.
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1.{{{(P+W)2=600}}}
2.{{{(P-W)2.5=600}}}
From eq. 1,
{{{P+W=300}}}
From eq. 2,
{{{P-W=240}}}
Add them to eliminate W,
{{{P+W+P-W=300+240}}}
{{{2P=540}}}
{{{highlight_green( P=270)}}}
Then from eq. 1,
{{{P+W=300}}}
{{{270+W=300}}}
{{{highlight_green(W=30)}}}
The speed of the plane in still air is 270 mph.