Aptitude Tests 4 Me

Basic Numeracy/Quantitative Aptitude

Detailed Solution

68. d: The correct answer is 13/28.
You can calculate the probability of picking two empty boxes. If you pick one box, you have a chance of 6/8 (=3/4) to find nothing inside. Then there are seven boxes left, of which five are empty, so there's a chance of 5/7 that your second box is empty as well. 3/4 x 5/7 = 15/28 to find nothing, which means 13/28 to find at least one present.

69. c: The correct answer is 19x18x17/59x58x57.
Mark has a 19/59 chance to be in the same class as Peter. Anne has an 18/58 chance to be in the same class as the first two, and Rose has a 17/57 chance to be in the same class as the other three

70. c: The correct answer is 4.
There are three colours, so if I only take three socks they can all have a different colour. As soon as I take a fourth one they can't all be different.

71. a: The correct answer is 10/21.
I have five chances out of seven to survive. If I do survive, there are six cups remaining of which two are poisoned. This would mean you have four chances out of six to survive as well(=2/3). 5/7 x 2/3 = 10/21.

72. d: The correct answer is 59,049/1,048,576.
He has three chances out of four for each question. 3/4 x 3/4 x 3/4 x 3/4 x 3/4 x 3/4 x 3/4 x ¾ x 3/4 x 3/4 = 59,049/1,048,576. 59,049 is the tenth power of three. 1,048,576 is the tenth power of four.

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