IIT JEE Practice Question and Answer

Q: Some children goto ice-cream shop. 9 flavours are available there. Each child takes a cone with two different flavours. No two children take same combination and they have taken all such possible combinations. How many children went to ice cream shop ? 1096 0

  • 1
    28
    Correct
    Wrong
  • 2
    56
    Correct
    Wrong
  • 3
    44
    Correct
    Wrong
  • 4
    36
    Correct
    Wrong
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Answer : 4. "36"
Explanation :

Answer: D) 36 Explanation: Given there are 9 flavours of ice creams.   Each child takes the combination of two flavours and no two children will have the same combination   This can be done by  ways i.e children.   Number of children=C29  = 9 x 8 / 1x 2 = 36.

Q: There are 6561 balls are there out of them 1 is heavy. Find the minimum number of times the balls have to be weighted for finding out the heavy ball ? 1046 0

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    2414
    Correct
    Wrong
  • 2
    204
    Correct
    Wrong
  • 3
    87
    Correct
    Wrong
  • 4
    8
    Correct
    Wrong
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Answer : 4. "8"
Explanation :

Answer: D) 8 Explanation: Suppose there are 9 balls   Let us give name to each ball B1 B2 B3 B4 B5 B6 B7 B8 B9   Now we will divide all the balls into 3 groups.   Group1 - B1 B2 B3   Group2 - B4 B5 B6   Group3 - B7 B8 B9   Step1 - Now weigh any two groups. Let's assume we choose Group1 on left side of the scale and Group2 on the right side.   So now when we weigh these two groups we can get 3 outcomes.   Weighing scale tilts on left - Group1 has a heavy ball.Weighing scale tilts on right - Group2 has a heavy ball.Weighing scale remains balanced - Group3 has a heavy ball.Lets assume we got the outcome as 3. i.e Group 3 has a heavy ball.   Step2 - Now weigh any two balls from Group3. Lets assume we keep B7 on left side of the scale and B8 on right side.   So now when we weigh these two balls we can get 3 outcomes.   Weighing scale tilts on left - B7 is the heavy ball.Weighing scale tilts on right - B8 is the heavy ball.Weighing scale remains balanced - B9 is the heavy ball.The conclusion we get from this Problem is that each time weigh. We element 2/3 of the balls.   As we came to conclusion that Group3 has the heavy ball from Step1, we remove 6 balls from the equation i.e (2/3) of 9.   Simillarly we do the ame thing for the Step2.   Now going with this conclusion. We have 6561 balls.   Step - 1   Divided into 3 groups   Group1 - 2187Balls   Group2 - 2187Balls   Group3 - 2187Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 2   Divided into 3 groups   Group1 - 729Balls   Group2 - 729Balls   Group3 - 729Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 3   Divided into 3 groups   Group1 - 243Balls   Group2 - 243Balls   Group3 - 243Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 4   Divided into 3 groups   Group1 - 81Balls   Group2 - 81Balls   Group3 - 81Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 5   Divided into 3 groups   Group1 - 27Balls   Group2 - 27Balls   Group3 - 27Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 6   Divided into 3 groups   Group1 - 9Balls   Group2 - 9Balls   Group3 - 9Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 7   Divided into 3 groups   Group1 - 3Balls   Group2 - 3Balls   Group3 - 3Balls   Taking the similar steps as we did in the above example, we come to the conclusion that Group1 has the heavy ball.   Step - 8   So now when we weigh 2 balls out of 3 we can get 3 outcomes.   Weighing scale tilts on left - left side placed is the heavy ball.Weighing scale tilts on right - right side placed is the heavy ball.Weighing scale remains balanced - remaining ball is the heavy ball.So the general answer to this question is, it is always multiple of 3 steps.   For 9 balls  32= 9. therefore 2 steps   For 6561 balls 38 = 6561 therefore 8 steps

Q: A,B,C together can do a piece of work in 10 days.All the three started workingat it together and after 4 days,A left.Then,B and C together completed the work in 10 more days.In how many days can complete a work alone ? 1507 0

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    25
    Correct
    Wrong
  • 2
    24
    Correct
    Wrong
  • 3
    23
    Correct
    Wrong
  • 4
    21
    Correct
    Wrong
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Answer : 1. "25"
Explanation :

Answer: A) 25 Explanation: (A+B+C) do 1 work in 10 days. So (A+B+C)'s 1 day work=1/10 and as they work together for 4 days so workdone by them in 4 days=4/10=2/5 Remaining work=1-2/5=3/5   (B+C) take 10 more days to complete 3/5 work. So( B+C)'s 1 day work=3/50 Now A'S 1 day work=(A+B+C)'s 1 day work - (B+C)'s 1 day work=1/10-3/50=1/25 A does 1/25 work in in 1 day Therefore 1 work in 25 days.

Q: A train covers a distance between station A and station B in 45 min.If the speed of the train is reduced by 5 km/hr,then the same distance is covered in 48 min.what is the distance between the stations A and B ? 1871 0

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    80 kms
    Correct
    Wrong
  • 2
    60 kms
    Correct
    Wrong
  • 3
    45 kms
    Correct
    Wrong
  • 4
    32 kms
    Correct
    Wrong
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Answer : 2. "60 kms"
Explanation :

Answer: B) 60 kms Explanation: Let 'd' be the distance and 's' be the speed and 't' be the timed=sxt45 mins = 3/4 hr and 48 mins = 4/5 hrAs distance is same in both cases;s(3/4) = (s-5)(4/5)3s/4 = (4s-20)/515s = 16s-80s = 80 km.=> d = 80 x 3/4 = 60 kms.

Q: When Ram was born, his father was 32 years older than his brother and his mother was 25 years older than his sister. If Ram's brother is 6 years older than Ram and his mother is 3 years younger than his father, how old was Ram's sister when Ram was born ? 2186 0

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    6 years
    Correct
    Wrong
  • 2
    8 years
    Correct
    Wrong
  • 3
    10 years
    Correct
    Wrong
  • 4
    12 years
    Correct
    Wrong
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Answer : 3. "10 years"
Explanation :

Answer: C) 10 years Explanation: Ram age when he was born = 0 years=> His brother's age = 6 year=> His father's age = brother age + 32years = 6+32 = 38=> His mother's age = father's age - 3 = 35So sister's age = 35-25 = 10years.

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Answer :
Explanation :

Out of 4 fruits, any 3 are chosen by 4 families.So the combinations areApple - A Cherries - C Banana - B Grapes - G1) ACB2) ACG3) BCG4) GAB By 2nd condition, Miller family uses either i)ACB or ii)ACGNow we have Robin, Mandy and Miller who uses apples (ACB,ACG,GAB)while Miller and Mandy both uses A and C. That leaves GAB for Robin. By 3rd condition Flure uses either C or G. So if we leave out the terms containing both C and G, we are left with ACB and GAB Now, for the time being let's suppose Robin is not a Flure.So ACB is taken by Flure. So ACG has to be Miller and that leaves BCG to be Clark. So we get Robin - Jacob(GAB). By 4th and 2nd conditions Erica and Mandy belong to the first two. That leaves Stacy - Clark(BCG). By 2nd condition Mandy is not a Miller, so we get Mandy - Flure(ACB) and that leaves Erica - Miller(ACG).

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Answer : 4. "31"
Explanation :

Answer: D) 31 Explanation: Let y be the total number of loavesa be the remaining loaves after 1st thiefb be the remaining loaves after 2nd thiefand c, d..so on after 3 and 4 the = 0 be the remaining loaves after 5th thief a = y - (y/2 + 1/2)= y/2 - 1/2 b = a - (a/2 + 1/2)= a/2 - 1/2 c = b - (b/2 + 1/2)= b/2 - 1/2 d = c - (c/2 + 1/2)= c/2 - 1/2 e = d - (d/2 + 1/2)= d/2 - 1/2we know that, e = 0,thus by substitution, we getd = 1c = 3b = 7a = 15y = 31Therefore total number of bread loaves in bakery was 31.

Q: A rectangular block has the dimensions 5x6x7 cm it is dropped into a cylindrical vessel of radius 6cm and height 10 cm. If the level of the fluid in the cylinder rises by 4 cm, What portion of the block is immersed in the fluid ? 2598 0

  • 1
    22/7 x 24/35
    Correct
    Wrong
  • 2
    22/7 x 36 x 4
    Correct
    Wrong
  • 3
    22/7 x 36/5
    Correct
    Wrong
  • 4
    22/7 x 37/21
    Correct
    Wrong
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Answer : 1. "22/7 x 24/35"
Explanation :

Answer: A) 22/7 x 24/35 Explanation: Since level of water increased in cylinder by height 4.  This is because of the rectangular block .   Therefore , area of rectangular block immersed in water is  = 227×6×6×4   Thats why portion of block immersed in water is  = (22/7 * 36 * 4) / total vol. of rectangle  = (22/7 * 36 * 4)/ (7*5*6)  = (22/7 * 24)/ 35.

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