Question

A mountaineer climbed 1,000 feet at a rate of x feet per hour. He climbed an additional 5,000 feet at a different rate. This rate was 10 feet per hour less than twice the first rate. Which expression represents the number of hours the mountaineer climbed

Answer 1

Your question asks for an expression, so you would expect an answer in the form of an equation containing variables. This is because you have only 2 independent equations with 3 unknowns. That makes the system unsolvable. 

Suppose v₁ is the mountaineer's velocity during the 1,000-foot trail. Then, v₂ is his speed for the 5,000-foot trail. The equation relating these two variables is:

v₂ = 2v₁ - 10 ---> equation 1

Then, you find the equation for the total number of hours he climbed. That would be the distance divided by their respective speed.

t = 1000/v₁ + 5000/v₂ ----> equation 2

Substituting equation 1 to equation 2,

t = 1000/v₁ + 5000/(2v₁ - 10)
t = 1000/v₁ + 5000/2(v₁-5)
t = 1,000/v₁ + 2,500/(v₁-5)