Question 134622
Divide the trip into 2 parts:
The 1st 40 min or 2/3 hr
The next 80 min or 4/3 hr
Call the distance covered on the 1st part {{{d}}}
The distance covered on the 2nd part is {{{160 - d}}}
Call the ground speed on the 1st part {{{s}}}
The ground speed on the 2nd part is {{{2s}}}
{{{d = s*(2/3)}}}
{{{160 - d = 2s*(4/3)}}}
Substitute {{{d}}} in the 1st for {{{d}}} in the 2nd
{{{160 - s*(2/3) = 2s*(4/3)}}}
multiply both sides by {{{3}}}
{{{480 - 2s = 8s}}}
{{{10s = 480}}}
{{{s = 48}}}mi/hr
{{{d = 48*(2/3)}}}
{{{d = 32}}}mi
The plane travelled 32 mi during the 1st 40 min
check:
{{{160 - d = 2s*(4/3)}}}
{{{160 - 32 = 2*48*(4/3)}}}
{{{128 = 128}}}
OK