What number comes next in the series?

5 15 5 18 5 24 14 20 _

If two's company, and three's a crowd, then whats four and five ?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

Take one out and scratch my head, I am now black but once was red. What am I?

I have nine bottles of wine and one of the nine bottles is poisoned.
I need to find the poisoned bottle with two facts
(1) Poison is deadly, only a sip will cost death
(2) I have two mice to do so.

How should I do it?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

Spot what is wrong here in below Picture?

There are four 3-link chains. All you have to do is join them into a big 12-link chain. For joining two closed links, one of the links must be cut and placed onto the other link for closing.

How many minimum links will you have to cut to make the big chain?