mathsy, 2 easy ways of getting approximate answers to 20 without a calculator:-
a) every power of 10 requires just over 3 powers of 2. Therefore 50 powers of 2 suggests between 15 and 16 powers of 10.
b) If you know that log 2 = 0.3010 (which you should!), then log 2^50 = 15.05. Again, about 15 powers of 10
By both methods, this gives me 16 digits in the answer.
Well, not entirely, but it is right if you've roundeded it. But the real question is... what is 1.414 more commonly expressed as?
Mathsy, yes, I did round it and I do I know what it is expressed as - just wanted to leave something in the puzzle for someone else!
Memento ??? where da u live ?
Tigeree, are the two questions connected?
Memento is an absolutely brilliant suspense movie about a guy with short-term memory loss. It's a really weird film that actually runs backwards and is pretty scary and hugely thought-provoking when you get into what is actually happening.
Me, I live in Devon, UK & sometimes Philippines
I like this one! Some good red herrings. Started off thinking about what time dad left home; what is the distance from school to home? did dad always manage to arrive exactly on time? why did he call his son "X"? Actually, none of it is relevant (but I do feel sorry for the poor boy branded with such a name)
Assumption: The definition of "passing" means from the moment the front of the train starts to pass until the moment that the end of the train finishes passing.
The trains initially are heading toward each other. Therefore, their combined speed is 72 + 45 = 117kph
It takes 30 seconds for them to pass, so the combined length of the trains is 117/120 km
When travelling in the same direction, the differential speed is only 27kph.
In order to travel 117/120km at 27kph, it will take:
(117/120) * (60/27) minutes = 2.1666 minutes = 2 minutes 10 secs