Number System - Study Mode

[#551] There are 50 boxes and 50 persons. Person 1 keeps 1 marble in every box, person 2 keeps 2 marbles in every 2nd box, person 3 keeps 3 marbles in every third box. The process goes on till person 50 keeps 50 marbles in the 50th box. Find the total number of marbles kept in the 50th box.
Correct Answer

(D) 93

Explanation

Solution: Marbles in the 50th box will be kept by 1st, 2nd, 5th, 10th, 25th and 50th person is a factor of 50. Number of marbles =1 + 2 + 5 + 10 + 25 + 50 = 93

[#552] The difference between the greatest and the least four digit numbers that begins with 3 and ends with 5 is :
Correct Answer

(D) 990

Explanation

Solution: According to the question, ⇒ The least number = 3005 ⇒ The greatest number = 3995 ⇒ Difference will be = 3995 - 3005 = 990

[#553] If in a three digits number the last two digits places are interchanged a new number is formed which is greater than the original number by 45. What is the difference between the last two digits of that number ?
Correct Answer

(D) 5

Explanation

Solution: Three digit number = 100x + 10y + z To make number after changing last two digit = 100x + 10z + y Now, 100x + 10y + z = 100x + 10z + y - 45 9z - 9y = 45 z - y = 5

[#554] Which of the following is a perfect square ?
Correct Answer

(C) 1046529

Explanation

Solution: By checking last 3 digits Then, last '3' digits of 1046 529 529 is a square of 23 Hence, this is correct option

[#555] While solving a problem, by mistake, Anita squared a number and then subtracted 25 from it rather than first subtracting 25 from the number and then squaring it. But she got the right answer. What was the given number ?
Correct Answer

(C) 13

Explanation

Solution: Let the given number be x According to the question, x 2 - 25 = (x - 25) 2 x 2 - 25 = x 2 + (25) 2 - 50x x = 13