# Race and time problem.

• Nov 8th 2012, 07:25 PM
hisajesh
Race and time problem.
In a km race, if A gives B a 40 m start, A wins by 19 seconds, but if A gives B 30 seconds start, B wins by 40 m. Find the time that each takes to run a km?
• Dec 20th 2012, 07:26 AM
hollywood
Re: Race and time problem.
This is just algebra, isn't it? Let \$\displaystyle t_A\$ be A's time for a kilometer and \$\displaystyle t_B\$ be B's time for a kilometer. Then the first condition is:

\$\displaystyle t_A = 0.96t_B - 19\$

The second condition is:

\$\displaystyle 0.96t_A = t_B-30\$

So the solution is \$\displaystyle t_B=150\$, \$\displaystyle t_A=125\$, i.e. A takes 125 seconds to run a kilometer and B takes 150 seconds to run a kilometer.

- Hollywood
• Jan 23rd 2013, 03:51 PM
hisajesh
Re: Race and time problem.
Sorry for the late response. can you explain in details how do you get to those equations.
• Jan 23rd 2013, 07:00 PM
hollywood
Re: Race and time problem.
It's pretty much just translating the words to equations. It's actually not easy - you have to think about what's happening in these races:

"if A gives B a 40 m start, A wins by 19 seconds"
so A runs 1km in 19 seconds less time than B runs 0.96km
\$\displaystyle t_A = 0.96t_B - 19\$

"if A gives B 30 seconds start, B wins by 40 m"
so A runs 0.96km in 30 seconds less time than B runs 1km
\$\displaystyle 0.96t_A = t_B-30\$

- Hollywood