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Vyshak
chetan2u
There is a 30 cm line marked at each cm and an insect is placed at every cm. 9 frogs are trained to jump a constant distance. the first one jumps 2cm in every leap, second one jumps 3cm and so on till 9th one jumps 10cm in every leap and they eat any insect that is available at that spot. If all of them start from start line and finish the entire 30cm, how many insects were still left after the race got over.
A) 0
B) 4
C) 6
D) 9
E) 10


I think the answer should be 7. Since all of them start from start line (if you see a ruler, the line starts from 0), and the minimum leap is 2 cm. So no frog jumps to 1 cm point. Answer should be 1 followed by primes greater than 10 and less than 30. i.e. 1, 11, 13, 17, 19, 23, 29.

yes the same doubt is also with me but i marked C because from my view it never exceeds 7. atleast it should be 6 in any other case.
also we have to consider any insect at 0 must be eaten by any frog.
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Vyshak
chetan2u
There is a 30 cm line marked at each cm and an insect is placed at every cm. 9 frogs are trained to jump a constant distance. the first one jumps 2cm in every leap, second one jumps 3cm and so on till 9th one jumps 10cm in every leap and they eat any insect that is available at that spot. If all of them start from start line and finish the entire 30cm, how many insects were still left after the race got over.
A) 0
B) 4
C) 6
D) 9
E) 10


I think the answer should be 7. Since all of them start from start line (if you see a ruler, the line starts from 0), and the minimum leap is 2 cm. So no frog jumps to 1 cm point. Answer should be 1 followed by primes greater than 10 and less than 30. i.e. 1, 11, 13, 17, 19, 23, 29.

Hi,
typo error..
9 was supposed to be 7..
Edited .. Thanks
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chetan2u
Vyshak
chetan2u
There is a 30 cm line marked at each cm and an insect is placed at every cm. 9 frogs are trained to jump a constant distance. the first one jumps 2cm in every leap, second one jumps 3cm and so on till 9th one jumps 10cm in every leap and they eat any insect that is available at that spot. If all of them start from start line and finish the entire 30cm, how many insects were still left after the race got over.
A) 0
B) 4
C) 6
D) 9
E) 10


I think the answer should be 7. Since all of them start from start line (if you see a ruler, the line starts from 0), and the minimum leap is 2 cm. So no frog jumps to 1 cm point. Answer should be 1 followed by primes greater than 10 and less than 30. i.e. 1, 11, 13, 17, 19, 23, 29.

Hi,
typo error..
9 was supposed to be 7..
Edited .. Thanks

Now the OA should be D

1,11,13,17,19,23,29
Toatal=7
Ans D
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chetan2u
There is a 30 cm line marked at each cm and an insect is placed at every cm. 9 frogs are trained to jump a constant distance. the first one jumps 2cm in every leap, second one jumps 3cm and so on till 9th one jumps 10cm in every leap and they eat any insect that is available at that spot. If all of them start from start line and finish the entire 30cm, how many insects were still left after the race got over.
A) 0
B) 4
C) 6
D) 7
E) 10


OA after 2 days

Answer must be 7

Frog 1 = 2, 4 , 6 , 8 , 10 , 12 , 14 , 16 , 18 , 2 0 , 22 , 24 , 26 , 28 , 30
Frog 2 = 3 , 6 , 9 , 12 , 15 , 18 , 21 , 24 , 27 , 30
Frog 3 = 4,8,12,16,20,24,28
Frog 4 = 5, 10 , 15 , 20 , 25 , 30
Frog 5 = 6, 12 , 18 , 24 , 30
Frog 6 = 7, 14 , 21 , 28

On scrutinizing it reveals the following frogs are left - 1,11,13,17,19,23,29
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chetan2u
There is a 30 cm line marked at each cm and an insect is placed at every cm. 9 frogs are trained to jump a constant distance. the first one jumps 2cm in every leap, second one jumps 3cm and so on till 9th one jumps 10cm in every leap and they eat any insect that is available at that spot. If all of them start from start line and finish the entire 30cm, how many insects were still left after the race got over.
A) 0
B) 4
C) 6
D) 7
E) 10


OA after 2 days

Hi,
the Q tests our CONCEPTS on number properties...
each frog is basically jumping on multiples of 2,3,4,5,6,7,8,9 and 10..
WHAT does it mean?
It means insects on multiples of these numbers will be eaten by these insects..
That will leave us with ONLY prime numbers OR multiple of PRIME numbers above 10..


SO
1) Prime numbers till 30 = 11,13,17,19,23,29 = 6..
2) multiple of PRIME numbers above 10- lowest will be 11*11= 121

But we have only 30 cm so NIL
NOTE- Had the length been 130, 121 also would have been taken into consideration

3) ofcourse no one touches the insect on 1 cm=1
total 6+0+1=7
D
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