distance over time

**simonmann** · May 28th 2008, 05:56 AM

a student walks y kilometres at 3km/h

i) write down an expression for the time, in hours that he takes.

ii) he then walks a further y+3 kilometres at 4km/h. the total walking time is 4 hours and 50 minutes. write down the equation in y and solve it.

**earboth** · May 28th 2008, 06:11 AM

Originally Posted by simonmann

a student walks y kilometres at 3km/h

i) write down an expression for the time, in hours that he takes.

ii) he then walks a further y+3 kilometres at 4km/h. the total walking time is 4 hours and 50 minutes. write down the equation in y and solve it.

$speed=\frac{distance}{time}$

Solve for time: $\frac{y}{t}=3~\implies~t=\frac y3$

The next part of his walk:

$\frac{y+3}t=4~\implies~ t=\frac{y+3}4$

Both periods together are $\frac{29}6\ h$

$\frac y3 + \frac{y+3}4 = \frac{29}6$

Solve for y. I've got: $\boxed{y = 7\ km}$

**masters** · May 28th 2008, 06:19 AM

distance = rate*time

$d=rt$

$t=\frac{d}{r}$

$t_1=\frac{y}{3}$
$t_2=\frac{y+3}{4}$

$t_1+t_2=\frac{y}{3}+\frac{y+3}{4}=\frac{29}{6}$

$4y+3y+9=58$

$7y=49$

$y=7km$

Too fast for me Earboth!!

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