If 21x = 79x, what is the value of x?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

Replace all '*' with digits 1, 2, 3, 4, 5 and 6 to make below statement true.

* *
x *
=====
* * *

Can you find out the remainder when 3^300 is divided by 5?

A man died, leaving $10,000,000 for his widow, 5 sons and 4 daughters. Each daughter received an equal amount, each son received twice as much as a daughter, and the widow received three times as much as a son.

How much did the widow receive?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

A car meter reading shows 72927 miles a palindromic number.
what is the minimum number of miles you would need to travel to see another palindromic number on the car meter reading?