Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

There is a hypothetical state between the USA and Mexico border 'Tango'.
Here 70 percent of the population have defective eyesight, 75 percent are hard of hearing, 80 percent have Nose trouble and 85 percent suffer from allergies, what percentage (at a minimum) suffer from all four ailments?

Why is a river so rich ?

Count the number of triangles in the given picture.

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

A new Engineering building containing 100 offices had just been completed. John was hired to paint the numbers 1 to 100 on the doors. How many times will John have to paint the number nine (9)?

What do you see in the image below

Can you find a number that lies one third of the distance between 1/3 and 2/3?

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

There is a five-letter word which has 3 consonants(all are same) and 2 different vowels.
Also, something wrong is associated with the word.

Can you name it?