What does this Rebus Picture means ?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

Why do we preferably have round manhole covers and not square ones?

John killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

I am the largest in my family of fifty.
The youngest of our family lives separately from the rest of the family and so do I.
I am regarded as harsh and tough.
I am so large, you cut me in two equal halves,
each half would still be larger than the second largest member of the family.
Who am I?

Take away the whole and some still remain. What is it?

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

Every words stands for unique digit that makes the arithmetic equation true

SEVEN + SEVEN + SIX = TWENTY.

What are the digits ?

What is wrong in the below Picture?

Can you calculate the probability of getting a sum of six when a dice is thrown twice?