x km at 8 km/hr and y km at 20 km/hr . His total time is 3.5 hours.
RATE TIME DISTANCE
SLOW 8 x
FAST 20 y
Total 3.5
Fill the missing cells and see what might be done if anything from that.
RATE TIME DISTANCE
SLOW 8 
x
FAST 20 
y
Total 3.5
The obvious equation is 
.
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Simplify this equation.
The "total" time taken to the cycle (2x+4) km at 8 km/hr and y/3 km at 20 km/hr is 5 hours.
That is saying 5 hours is "total time"; and then ..... this is a different description, going like this:
? 8 2x+4
? 20 y/3
total 5
to be filled this way:
RATE TIME DISTANCE
? 8 
2x+4
? 20 
total 5
The only obvious equation for this part of the description is
simplifiable to
The two equations found as a system are this one:
Solve this system.
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(This would give x=16.)
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scratch work
2*2*2, 2*2*3*5
2*2*2*3*5 LCD
(