Find the next number in the series 125, 80, 45, 20, ....

 

Here by trial and error method, we can obseve that

404404 = 404 x 1001; 415415 = 415 x 1001, etc.

So, any number of this form is divisible by 1001.

On dividing 627349 by 15, we get remainder = 4.
Therefore, the obtained remainder is the least number to be subtracted from the given number so that the the mnumber is divisible by 15.
Here 4 is the least number to be subtracted from 627349 so that it is divisible by 15.

we can treat every two consecutive terms as one.
So, we will have a total of 100 terms of the nature:
(2 + 5) + (7 + 6) + (12 + 7).... => 7, 13, 19,....

We know the sum of n terms  nn+12

Now, a= 7, d=6 and n=100
Hence the sum of the given series is
S= 100/2 x[2 x 7 + 99 x 6]
=> 50[608]
=> 30,400.

we can do this by trial and error method.

Putting x = 2,we get 2²(2² - 1) = 12.
checking with other integers, the above equation always gives a value which is a multiple of 12,
So, x²(x² - 1) is always divisible by 12.

Since 653xy is divisible by 5 as well as 2, so y = 0.
Now, 653x0 must be divisible by 8.
So, 3x0 must be divisible by 8. This happens when x = 2
x + y = (2 + 0) = 2.

The pattern is -4, +9,-16, +25, -36

The next number=119+49=168

The pattern is 32+42=52,  52+122=132, 72+242=252 

The next number = 82+152=172

 i.e. 17

The pattern is 12 22, 32 42, 52 62, 

∴The next number= 72 82= 4964