OG 31

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Junior | Next Rank: 30 Posts
Posts: 15
Joined: Sun Jun 08, 2008 5:12 pm

OG 31

by ssraf » Wed Jun 11, 2008 6:42 am
If Juan takes 11 seconds to run y yards, how long will it take him to run x yards at the same speed?

a)11x/y
b)11y/x
c)x/11y
d)11/xy
e)xy/11
Source: — Problem Solving |

Junior | Next Rank: 30 Posts
Posts: 15
Joined: Sun Jun 08, 2008 5:12 pm

by ssraf » Wed Jun 11, 2008 7:23 am
....

t= d/r

d=x

r= y/11 (same as y)

therefore, x/y/11= 11x/y

Junior | Next Rank: 30 Posts
Posts: 11
Joined: Sat Jun 07, 2008 11:09 am

by manu217 » Thu Jun 12, 2008 7:28 am
This is good solution. Another way to do it:

y yards -- > 11 sec
x yards --> A secs

Cross multiplying ==> A= 11x/y

Of course this works only because speed is constant so we can use the principle of proportion.