What is at the end of a rainbow?

I welcome the day with a show of light, I stealthily came here in the night. I bathe the earthy stuff at dawn, But by noon, alas! I'm gone.

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.

John is selling fruits.
He sells grapes at $30, Dates $25, and a Wolfberry $45.
At what price does he sell fig?

PS: Logical Thinking

I’m light as a feather, yet the strongest person can’t hold me for five minutes. What am I?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

If a shopkeeper can only place the weights on one side of the common balance. For example, if he has weights 1 and 3 then he can measure 1, 3 and 4 only. Now the question is how many minimum weights and names of the weights you will need to measure all weights from 1 to 1000? This is a fairly simple problem and very easy to prove also.

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

A brand new Mobile Phone was on sale at 20% as a promotional offer. By what per cent must the Mobile price be increased to sell it at the original price again?

What is more useful when it is broken?