Sherlock Holmes was challenged to make a pre-drawn line smaller without erasing it. He did it in fractions of seconds. How?

I have two sand hourglasses:
1. A 7 minute one and
2. An 11-minute one.

Using just these 2 sand hourglasses, how can I measure time as 15 minutes?

Analyze and find the missing item in the sequence:
16, 06, 68, 88, __, 98

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

I am the first thing you need while camping.
I am always with the person named Marcos Valencia and Carrick.
But Pogba Zlatan and Rooney think I am wasteful and do not need me.
I am the second to the last thing to add when you are making a patch.

What am I?

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?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

A father's child, a mother's child, yet no one's son.

Who am I?

Alex opened 24 presents
Jonah opened 8 presents
Clara opened 1 present

Can you find out how many presents were opened by Candy?

They are three errirs in this question. Can you find them?