Problem of the Day 12 Oct 2011

How many factors of  have last digit 2?

Problem of the Day 10 Oct 2011

Ten identical boxes of dimensions  are stacked flat on top of each other, with the orientation of each box being independent and random. If  is the probability that the height of the stack is  and , find . All units are in feet.

Problem of the Day 29 Sept 2011

Let a, b, c be three distinct odd natural numbers. Which of the following can be the sum of the squares of a, b and c?

(a) 3333                            (b) 5555                                (c) 9999                        (d) 7777

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Problem of the Day 23 Sept 2011

Darryl has a six-sided die with faces 1; 2; 3; 4; 5; 6. He knows the die is weighted so that one face
comes up with probability 1/2 and the other five faces have equal probability of coming up. He
unfortunately does not know which side is weighted, but he knows each face is equally likely
to be the weighted one.

He rolls the die 5 times and gets a 1; 2; 3; 4 and 5 in some unspecified order. Compute the probability that his next roll is a 6.



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Problem of the Day 22 Sept 2011

Susan plays a game in which she rolls two fair standard six-sided dice with sides labeled one through six. She wins if the number on one of the dice is three times the number on the other die. If Susan plays this game three times, compute the probability that she wins at least once.

Problem of the Day 19 September 2011

Two mathematicians take a morning coffee break each day. They arrive at the cafeteria independently, at random times between 9 a.m. and 10 a.m., and stay for exactly  mintues. The probability that either one arrives while the other is in the cafeteria is  and where  and  are positive integers, and  is not divisible by the square of any prime. Find 

Problem of the day 25.07.09

In 1896 lord Coin has decided to play a game. From the January 1 till December 31 every day he chooses among two match boxes an arbitrary one and placed a match from it to another box (if the chosen box was not empty). If the chosen box was empty then he placed a match from
the other box to the chosen one. What is the probability that after the December 31 the both boxes will have an equal number of matches if at the beginning each box had a) n = 400 b) n = 200 c) n = 100 matches?

Problem Of The Week 42

Let their be 7 special coins such that they are numbered from 1-7 on one side and blank on the other side. You toss all the 7 and let them fall and make your best guess as to which coin is 1, what is the probability that you are correct?

Problem Of The Week 31

A parking lot has 16 spaces in a row. Twelve cars arrive, each of which requires one parking space, and their drivers chose spaces at random from among the available spaces. Auntie Em then arrives in her SUV, which requires 2 adjacent spaces. What is the probability that she is able to park?

Problem Of The Week 28

Twenty five of King Arthur's knights are seated at their customary round table. Three of them are chosen - all choices being equally likely - and are sent of to slay a troublesome dragon. Let p be the probability that at least two of the three had been sitting next to each other. If p is written as a fraction in lowest terms, what is the sum of the numerator and the denominator?

Problem Of The Week 20

A classroom has 4 tables, each of which has 4 chairs. There are 16 students in the class, 4 of whom are friends. If the teacher assigns the seats randomly to the students, what is the probability that the 4 friends will be sitting together at a table?

Tipster: To every probability question, there are two parts, one to find the total possible roster and the other, to find the ones which suit our case( or the ones which not). We can't just find one and leave the other.

Problem Of The Week 17

Two points are selected randomly on the surface of a sphere of radius R. What is the expected distance between them, along the surface of the sphere?

Problem is simple if you think logically, else you will have issues. This question is taken from teh CAT quant Blog by Suresh, the link of which you can see on the right!

Tipster:  The sum of the two legs of a right angled triangle is equal to sum of diameters of incircle and circumcircle :)

Problem Of The Week 11

Triangle ABC is right angled at C. m<ABC=60 and AB=10. Let P be a point randomly chosen inside triangle ABC, such that BP extended meets CA at D. What is the probability that BD>5root(2)?