Theory of Numbe...

How many positive numbers less than 100 have all even digits?

For how many two-digit numbers is the sum of the digits greater than the product of the digits?

Consider 4-digit numbers for which the first two digits and the last two digits are equal. How many such numbers are perfect squares?

72 hens cost Rs. a96.7b, where two digits in place of 'a and b' are not visible as they are written in illegible handwriting. How much does each hen cost?

What is the smallest number which when multiplied by 1944 will make it a perfect square?

If n^m leaves a remainder of 1 after being divided by 7 for all positive integers n that are not multiples of 7, then m could be equal to

There are two lights. The first light blinks 3 times per minute, while the other blinks 5 times in two minutes. Find the number of times they will blink together in an hour.

An electric wire is sold only in multiples of m and a customer requires several lengths of wire, each 85 cm long. To avoid any wastage and to minimise labour, he should purchase minimum lengths of

Three bells chime at intervals of 18 min, 24 min and 32 min, respectively. At a certain time, they begin to chime together. What length of time will elapse before they chime together again?