John runs to the market and comes back in 15 minutes. His speed on the way to the market is 5m/s and his speed on the way back is 4m/s. Find the distance to the market.

The distance to the market is 2000 m

Step-by-step explanation:

∵ John runs to the market and comes back in 15 minutes

→ Change the min. to the sec. because the unit of his speed is m/s

∵ 1 minute = 60 seconds

∴ 15 minutes = 15 × 60 = 900 seconds

→ Assume that t1 is his time to the market and t2 is his time from

  the market

∵  t1 + t2 = 15 minutes

∴ t1 + t2 = 900 ⇒ (1)

→ Assume that the distance to the market is d

∵ His speed on the way to the market is 5m/s

∵ Time = Distance ÷ Speed

∴ t1 = d ÷ 5 ⇒ (1 ÷ 5 = 0.2)

∴ t1 = 0.2d ⇒ (2)

∵ His speed on the way back is 4m/s

∴ t2 = d ÷ 4 ⇒ (1 ÷ 4 = 0.25)

∴ t2 = 0.25d ⇒ (3)

→ Substitute (2) and (3) in (1)

∵ 0.2d + 0.25d = 900

∴ 0.45d = 900

→ Divide both sides by 0.45

∴ d = 2000 m

∴ The distance to the market = 2000 m

let's add {f(x)=x+1}f(x)=x+1 and {g(x)=2x}g(x)=2x together to make a new function.

f(x)+g(x) =(x+1)+(2x)=x+1+2x=3x+1

let's call this new function hh. so we have:

{h(x)}={f(x)}+{g(x)}{=3x+1}h(x)=f(x)+g(x)=3x+1

we can also evaluate combined functions for particular inputs. let's evaluate function hh above for x=2x=2. below are two ways of doing this.

method 1: substitute x=2x=2 into the combined function hh.

h(x)

h(2)

​    

=3x+1

=3(2)+1

=7

​ since h(x)=f(x)+g(x)h(x)=f(x)+g(x), we can also find h(2)h(2) by finding f(2) +g(2)f(2)+g(2).

first, let's find f(2)f(2):

f(x)

f(2)

​    

=x+1

=2+1

=3

​  

now, let's find g(2)g(2):

g(x)

g(2)

​    

=2x

=2⋅2

=4

​  

so f(2)+g(2)=3+4=\greend7f(2)+g(2)=3+4=7.

notice that substituting x =2x=2 directly into function hh and finding f(2) + g(2)f(2)+g(2) gave us the same answer!