If the highest common factor (HCF) of x and y is 15, then the HCF of 36x² − 81y² and 81x² − 9y² is divisible by _______.

What will come in place of the question mark (?) in the following equation, if ‘+’ and ‘−’ are interchanged and ‘÷’ and ‘×’ are interchanged? 4515 × 5 − 431 ÷...

In the following number-pairs, the second number is obtained by applying certain mathematical operations to the first number. In three of the four pairs, the sa...