Maths homework

[Beetroot]

4 friends need to cross a bridge
they start on the same side of the bridge a maximum of two people can cross at anytime. It is night and they have jsut one lamp. People that cross the bridge must carry thelamp to see the way.
A pair must walk together at the rate of the slower person
Rachel takes one minute to cross
Ben takes two minutes to cross
george takes 7 minutes to cross
and Yvonne takes 10 minutes to cross

The fastest time they all get across takes 17 minutes

Can you work out how it is done?

baffling all of us here

?

fastest time i can get is 21 mins.... r + b = 2mins... then r 1 min back.... then r + g =7 mins then r 1 min back then r + y = 10 mins = 21 mins

but then i'm pretty crap at maths? what year is dc in?

Yes, I know this one...... but can't remember off-hand . Got a feeling a couple have to go together and return, and maybe one goes halfway and then comes back........? Will ask DH. He'll know. Hang on

Hmm. ds says to throw the lamp back.

If Georga end Yvonne go together, that takes 10 mins, George throws lamp back, Rachel and Ben go together, taking 2 minutes. It takes them 12 minutes in total.

We can't see how it works.

It takes 17 minutes to get George and Yvonne across. Even if they go together then George still has to come back which brings you to 17 minutes.

R & B cross, 2mins
R returns, 1 min
G & Y cross 10 mins
B returns 2 mins
R & B cross 2 mins

oh well done nn! it's obvious to me NOW!

Aaaaaaah!

oh yes - oh yes - very good