...solve these riddles. If you can, I will be very thankful

1:
Aaron, Bob, Cindy & Danny (or A,B,C,D if you like) got lost in the dark. They see a town in the distance, but they have to cross a long bridge to get to it. It's pitch black out there, and all they have is one cellphone with enough light to lead the way, but the cellphone's battery is weak and will only last for another 100 minutes. There's no signal in the phone.
The bridge is narrow and only two of them can cross it at a time, and it's also dark, so they have to cross it with the cellphone's light.
Aaron is an acrobat and can cross the bridge within 5 minutes.
Bob is a young man, and it takes him 10 minutes to cross.
Cindy is afraid - it takes her half an hour to cross.
Danny is old - it takes him 1 hour to cross.
Since they have only one light source, they need to travel together, at the slower person's rate.
The bridge is too long to throw the cellphone over.
Can they make it? How? How long will it take?

2:
0
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M.D.
Ph.D.
B.Sc.

3:
A spy finds himself in a lighthouse. At the bottom of the lighthouse, there are 3 electric switches, and at the top of the lighthouse 3 spotlights with halogen light bulbs. He needs to signal his commander, but to do that, he needs to find out which switch controls which spotlight. He can only get out of the lighthouse and then come back in once, because otherwise the guard will find it suspicious, and might find out that he's a spy.
How can he do it? Needless to say, he can't see the spotlights from the bottom of the lighthouse - he needs to get out (and pass the guard), and he can't climb to the top. He can tell which spotlight is which, even when they are off.

4:
Find an English word with 5 letters that if you omit all but the first letter, you still get the same pronunciation.
Find an English word with 5 letters that if you omit all but the last letter, you still get the same pronunciation.

5:
You have an old set of scales, you know, the ones with two containers at each side. It only tells you whether the weight in the two containers is equal, or if the left side is heavier than the right side, or the right side is heavier than the left side.
You are given 12 coins that seems identical. 11 coins have the same weight, and 1 has a different weight. It can be either heavier or lighter than the rest.
Your mission is to identify which coin has the different weight, and to find out if it's heavier or lighter than the rest.
You can only use the scales 3 times!
Explain how

And number 3... Turn on one switch, wait, then turn it off. Now flip on a different one and go up to the top of the light house. There will be a lit bulb, a warm bulb, and a cold bulb. Now use the info gathered to determine which bulb goes with which switch.

Hey,

I am a new member for this forum. This is the first puzzle am trying to solve. I would try for 5.

Take 10 coins and drop five in each of the container. The three choices are: Either they are equal, the one in the right is heavier or the one in the left is heavier. If they are equal, weigh the remaining two which gives the desired result. Else, choose 4 coins from the lighter container and weigh two in each container. They can again be equal or one of the containers may have the lighter coin. If equal, the left out is the counterfeit. Else, weigh the coins again which are in the lighter container.

Hope this solves.....