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race

by shibal » Thu Jul 16, 2009 4:16 am
A and B ran a race of 480 m. In the first heat, A gives B a head start of 48 m and beats him by 1/10th of a minute. In the second heat, A gives B a head start of 144 m and is beaten by 1/30th of a minute. What is B’s speed in m/s?

OA 12
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by kaulnikhil » Thu Jul 16, 2009 1:25 pm
let a and b take x and y sec respt to run the race of 480 mts
therefore
x + 6 = (432/480)*y
and
x = (336/480)*y +2

solve for y u get y = 40 sec
speed of b = 480/10 = 12
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by xilef » Thu Jul 16, 2009 3:03 pm
Where am I going wrong here?

t=d/s

432/SB - 480/SA = 6
336/SB - 480/SA = 2

Solve for SB:

SB=24m/s
SA=40m/s
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by tohellandback » Thu Jul 16, 2009 3:18 pm
xilef wrote:Where am I going wrong here?

t=d/s

432/SB - 480/SA = 6
336/SB - 480/SA = 2

Solve for SB:

SB=24m/s
SA=40m/s
its your second line:
336/SB - 480/SA = 2
it should be
480/SA-336/SB =2.
The powers of two are bloody impolite!!
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by xilef » Thu Jul 16, 2009 3:22 pm
Ahhh, a perfect example of how crucial it is to read the question carefully. Thanx!
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