What occurs twice in a week, once in a year but never in a day?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

John was born on March 5, 1970, in Delhi, India. Jacob was born 25 days before John. The year when they took birth, Republic Day fell on Monday.

Can you find out on what day was Jacob born?

A pond had 60 fish, out of which, all but 20 died.
How many fishes are now present in that pond?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

John named his first son Alpha, second Beta, third Charlie and fourth Delta. What is the fifth son's name?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes