Member: reinout-g

erika06:
Yoshi's job interview is at 9:30 A.M. The 8-mile bus ride from his apartment to the job site takes 45 minutes, and Yoshi requires 45 minutes to wake up, dress, and get to the bus stop. What is the latest possible time that Yoshi should set his alarm clock for?

I think you can solve this if you try a little harder. 45minutes + 45 minutes = 90 minutes.

Now if Yoshi needs to wake up 90 minutes before 9:30 A.M., what time would that be?

reinout-gMar 12, 2014

+2353

Guest:
the bases and the height of a trapezoid with base lenghts 4 in. and 8 in. are all multiplied by 1/8.

I'm sorry to say that you're posing a statement instead of a question.

Do you want to know the area?

The length of the bases and the height?

A drawing of what it looks like?

Please be a little more specific.

Reinout

reinout-gMar 12, 2014

+2353

BLAHBLAHUN:
Dawn will get $780 more if her salary is increased by 12%. Dawn's colleague Su Lin's salary is 9% more than Dawn. What is Su Lin's salary?

We know two things,

1) 780 is 12% of Dawn's salary

2) Su lin earns 9% more than Dawn

We can calculate Dawn's salary by computing the following.

We know $780 is 12% of the salary so 1% of Dawn's salary is 780/12 = $65

We know $65 is 1% of the salary so 100% of Dawn's salary is $65*100 = $6500

Now Su lin earns 9% more than Danw so
Su lin's salary is $6500 + 9% of $6500 = $6500 + 9/100 * $6500 = $6500 + 0.09*$6500 = $7085

Now I computed this in a very slow and precise matter for the purpose of explanation but we can also do the following.

780/0.12 * 1.09 = $7085

Why?

Look at the following;

if we wanted to know 12% of $6500 we would have multiplied $6500 by 12/100 (which is 0.12)

Now similarly if we want to know the opposite (so we know 12% is 780 and we want to know 100%) we can divide by 0.12 instead of multiply (since division is the opposite of multiplication)

Now for the multiplication by 1.09, we know that Su lin has 9% more salary.

So as I showed before Su lin's salary is $6500 + 9% of $6500 = $6500 + 9/100 * $6500 = $6500 + 0.09*$6500

which gives 6500 + 0.09*6500 = (1+0.09) * 6500 = 1.09 * 6500 = 1.09 * 780/0.12

If you want to know more about percentages, these might help;

http://www.mathsisfun.com/percentage.html

http://www.mathsisfun.com/decimal-fraction-percentage.html

Reinout

reinout-gMar 12, 2014

+2353

sander:
Oh, wow sander. You are so smart!!!

Haha I hope I don't ruïn your day if I tell you the answer is {(x,y) E R ²: x+y = 12}
which is the set of all x and y that amount to 12 which also includes eg. (2,10) and (-4 16).

If I got you curious, here's some more
http://www.mathsisfun.com/sets/sets-introduction.html

Reinout

reinout-gMar 12, 2014

#25

+2353

Melody:
*
Hard one :
Three kids named Brooks, Clint and Riley have a new game using water balloons.
They each take turns trying to throw one balloon at one of the other two. If they hit, the person is out, otherwise the next person may take his turn.

Brooks hits 1/3 of the time, Clint hits 2/3 of the time and Riley never misses.
Brooks is allowed to start, then Clint (given that he is still in the game), then Riley (given that he is still in the game), etc.
Where should brooks aim during his first turn?

Well if Brooks misses both targets then Clint will definitely try to hit Riley. Because if Clint hits Brooks, Riley will get him next anyway.
Therefore there is no point in Brooks going for Clint.
Now if Brook hits Riley then Brook has a 2/3 chance of being hit next
If Brook misses altogether then he has no chance of being hit next, If Clint hits Riley then it is Brooks turn next anyway (he'll get another shot at clint). If Brook misses Riley then there is probably a less than 2/3 chance that Riley will target Brook next.

So it seems to me that Brook's best strategy is to purposefully miss both targets.

IS that right ??
--------------------------------------------------------------------------------------------------------------------------------------

Easier one: (still to be solved)
There are 31,542 people attending a concert. One person is picked from the audience and if his birthday is a monday he will win $1.000.000
What are the odds that that persons birthday is a monday?

Er let me see... There are seven days in the week. Everyone has to be born on one of them.
So the chance of anywone being born on a monday is 1/7
-----------------------------------------------------------------------------------------------------------------------------------------

Well done melody!

I like how you explained your reasoning.

I will see whether I can post some new ones a little later today

reinout-gMar 12, 2014

#18

+2353

Melody:
reinout-g wrote:New puzzle!
Three rivalling coaches (Pierre, Pieter and Peter) and their three athletes (Édouard, Eduard and Edward) want to cross a river.
There is only one boat which can carry two persons.
The coaches do not want other coaches to be with their athlete without they themselves beeing present at any moment..
How can they cross the river?

Same as before. We have three coaches C1, C2, and C3
and we have 3 athletes A1, A2, A3

So A1, A2, A3, C1, C2, C3 all have to get accross the river
A1, and C1 paddle across and A1 stays on the other side (C1 returns)

So A2, A3, C1, C2, C3 all have to get accross the river
C1, and C2 paddle across and A1 AND C1 stays on the other side (C2 returns)

So A2, A3, C2, C3 all have to get accross the river
C2, and C3 paddle across and C1, C2 and C3 stays on the other side (A1 returns)

So A1, A2, A3, all have to get accross the river
A1, and A2 paddle across and A1, C1, C2 and C3 stays on the other side (A2 returns)

So A2, A3, all have to get accross the river
A2, and A3 paddle across and everyone is on the other side