How can you make number one disappear by adding something to it?

While house hunting in London, I came across a very good leasehold property Discussing the lease the landlady told me:

'The property was originally on a 99 years lease and two-thirds of the time passed is equal to four-fifths of the time to come. Now work it out for yourself and see how many years are to go!

If it took eight men ten hours to build a wall, how long would it take four men to build it?

Through your logical capabilities, can you make 7 an even?

When I asked a girl's name she told me her name is the date '07/09/2001'.

I thought for a few seconds and then I got her name. Do you?

What do you see in the image below

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

One day Jenifer meets the Lion and the Tiger in the Forest of Forgetfulness. She knows that the Lion lies on Mondays, Tuesdays, and Wednesdays, and tells the truth on the other days of the week. The Tiger, on the other hand, lies on Thursdays, Fridays, and Saturdays, but tells the truth on the other days of the week. Now they make the following statements to Jenifer:

Lion: Yesterday was one of my lying days.

Tiger: Yesterday was one of my lying days too.

What day is it?

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?

What kind of band never plays music?