Thursday, 13 December 2007

That maths problem...

For Mr Hanley's maths group (and for Miss McCarney's if you fancy a challenge):

A 2 litre jar of water is left on a shelf. 20% evaporates per day. How much will be left at the end of each day for the first 5 days?

HINT: The answer is not 1 litre - think about how much 20% of the water will be on each day.

11 comments:

Anonymous said...

The answer is 1 litre

Anonymous said...

I think 1litre would be left because 20*5=100 and that would be 1litre / 2=1litre.
Ayan

Anonymous said...

2000 ml is 2l
so 20% is 20/100
2000/100*20=400ml_evaporates
2000-400=1600ml_day 1
1600/100*20=320_evaporates
1600-320=1280ml_day 2
1280/100*20=256ml_evaporates
1280-256ml=1024ml_day 3
1024/100*20=204.8_evaporates
1024-204.8=819.2_day 4
819.2/100*20=163.84_evaporates
819.2-163.84=655.36ml
=0.65536l
that is the answer
Raneem

Anonymous said...

so is that correct i hope so
raneem

Mr Hanley said...

Well worked out, Raneem!

Your answer is correct and your working-out was useful.

Of course, another way to find out what a value minus 20% is, is to find 80% of that value. So - 2000ml x 0.8 = 1600ml would work out the first day nice and quickly.

Well done!

Anonymous said...

wow your really clever raneem i am proud to be your friend.
keep it up!!!!!!!!!!!!

Anonymous said...

i did not know
your so clever

Anonymous said...

mr hanley can you put some extra hard work on the blog

Anonymous said...

it is impossible to beat 36 in the times table! My highest is 30.

now I'll try losing

Anonymous said...

=0.65536L!!!!!!!!!!!

Anonymous said...

some one has done it in my name in the timetable challenge and the scores are only 2 and 9