Time, Speed & Distance
Aptitude

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Q.

A race course is 400 m long. $A$ and $B$ run a race and $A$ wins by 5m. $B$ and $C$ run over the same course and $B$ win by 4m. $C$ and $D$ run over it and $D$ wins by 16m. If $A$ and $D$ run over it, then who would win and by how much?

 A.

$D$ by 7.2 m

 B.

$A$ by 7.2 m

 C.

$A$ by 8.4 m

 D.

$D$ by 8.4 m

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Solution:
Option(A) is correct

If $A$ covers 400m, $B$ covers 395 m

If $B$ covers 400m, $C$ covers 396 m

If $D$ covers 400m, $C$ covers 384 m

Now if $B$ covers 395 m, then $C$ will cover \(\dfrac{396}{400}\times 395=391.05\)m

If $C$ covers 391.05 m, then $D$ will cover \(\dfrac{400}{384}\times 391.05 = 407.24\)

If $A$ and $D$ run over 400 m, then $D$ win by 7.2 m (approx.)

Edit: For an alternative solution, check comment by Vejayanantham TR.


(5) Comment(s)


Vaibhav Varish
 ()

Sa-Speed of a in meter/minute

eq1---

400/Sb-400/Sa=5

eq2---

400/Sc-400/Sb=4

eq3--

400/Sc-400/Sd=16

adding 1&2--

400/Sc-400/Sa=9;

eq3-eq2---

400/Sa-400/Sd=7

that' s why D wins by 7 min why 7.2 (Whats wrong in my solution)..pls help



Vejayanantham TR
 ()

A - 5m

B - 4m

D -16 m

We need to find from A -> D

A->B->C = 5+4

D -> 16m

16-9 = 7 => D wins by 7m (approx)


Manohar Tangi
 ()

please elaborate.....

Nayak Sowrabh
 ()

Since the number 16 is too small in comparison to 400 u get an approximate value to be 7.

If it was a 100meter race then u would have got the answer to be -> D wins the race by 8.5m.

This is because 16 makes a lot of difference to the number 100.

so we cannot use this methodology in all those cases.

Yogesh
 ()

can we apply this method on these type of question