Join the Unexplained Mysteries community today! It's free and setting up an account only takes a moment.

# Mathematics Brain Teasers.

## Recommended Posts

@Guyver, would you like to try and answer the above question? I remember you setting afew statistical questions for me once in another thread

• Replies 426
• Created

• 166

• 144

• 42

• 25

#### Posted Images

13 hours ago, Ozymandias said:

In a given population 57% are female; 62% are unemployed; and 44% are at least 40 years old. What is the probability that any person randomly chosen from this population will be an employed male under 40 years of age?

Hint: Because some or all of these categories can exhibit in any given individual the multiplication rule applies and the probabilities for each relevant category mutiplies the other relevant categories for that individual.

##### Share on other sites

@Habitat are you interested in doing this one? It's a probability question.

##### Share on other sites

On 15/11/2018 at 11:05 PM, Ozymandias said:

In a given population 57% are female; 62% are unemployed; and 44% are at least 40 years old. What is the probability that any person randomly chosen from this population will be an employed male under 40 years of age?

Well, it's been over two days and more than 60 views and nobody wants a go, so here is the answer:

Writing probabilities as decimal fractions and noting that each category listed has a complement (i.e. every person either complies with it or doesn't):

Female (0.57) - Male (0.43)

Unemployed (0.62) - Employed (0.38)

40 or more (0.44) - Less than 40 - (0.56)

So, the probability of being male and employed and under forty is:

0.43 x 0.38 x 0.56 = 0.091504 or 9.15%

##### Share on other sites

I was going to leave it open for a while because it was quite easy, you basically gave the method in your hint. But some people don't frequently visit and I was hoping someone might pop in and participate.

If you want to set another question and leave it open ended you can do that. If you don't I have my old Texts and Tests leaving cert book I'll rob a question from that and leave it up.

##### Share on other sites

How many triangles?

• 1
##### Share on other sites

• 1 month later...

36?

• 1
##### Share on other sites

• 2 months later...
On ‎18‎/‎11‎/‎2018 at 8:27 AM, danydandan said:

How many triangles?

44

• 1
##### Share on other sites

15 minutes ago, RabidMongoose said:

44

Yeap.

16+8+8+4+2+2+2+2 = 44.

You can set a Mathematics based brain teaser.

##### Share on other sites

Add one line to this equation to make it right

5 + 5 + 5 + 5 = 555

Edited by RabidMongoose
##### Share on other sites

2 hours ago, RabidMongoose said:

Add one line to this equation to make it right

5 + 5 + 5 + 5 = 555

There are four possible answers of which three are similar, although somewhat unsatisfactory, and the fourth is unique.

Edited by Ozymandias
• 1

5 X 100 + 5 X 7

##### Share on other sites

11 hours ago, Ozymandias said:

There are four possible answers of which three are similar, although somewhat unsatisfactory, and the fourth is unique.

That didnt last long, please post one of them so it can be your turn.

##### Share on other sites

1 hour ago, RabidMongoose said:

That didnt last long, please post one of them so it can be your turn.

The four possible answers I mentioned earlier are:

(1) 5 4 5 + 5 + 5 = 5 5 5

(2) 5 + 5 4 5 + 5 = 5 5 5

(3) 5 + 5 + 5 4 5 = 5 5 5

(4) 5 + 5 + 5 + 5 =/= 5 5 5  [Note; =/= is the equal sign with a stroke through it, meaning 'is not equal to']

Edited by Ozymandias
• 3
##### Share on other sites

20 minutes ago, Ozymandias said:

The four possible answers I mentioned earlier are:

(1) 5 4 5 + 5 + 5 = 5 5 5

(2) 5 + 5 4 5 + 5 = 5 5 5

(3) 5 + 5 + 5 4 5 = 5 5 5

(4) 5 + 5 + 5 + 5 =/= 5 5 5  [Note; =/= is the equal sign with a stroke through it, meaning 'is not equal to']

##### Share on other sites

1 hour ago, RabidMongoose said:

OK, being an economist (I think?) this one is specially for you and only involves ratio and proportion:

A factory having six identical production lines manufactures laser printers.  Working steadily, continuously and normally any 5 of its production lines can manufacture 200 laser printers in 3 hours. With all production lines operating in like manner how many printers can this factory produce in an 8 hour shift?

##### Share on other sites

On ‎09‎/‎03‎/‎2019 at 3:42 PM, Ozymandias said:

A factory having six identical production lines manufactures laser printers.  Working steadily, continuously and normally any 5 of its production lines can manufacture 200 laser printers in 3 hours. With all production lines operating in like manner how many printers can this factory produce in an 8 hour shift?

Any takers. I thought that this was right up Rabid Mongoose's alley, he being an economist (I think?)

##### Share on other sites

17 hours ago, Ozymandias said:

Any takers. I thought that this was right up Rabid Mongoose's alley, he being an economist (I think?)

Eh.

Around 2880?

Each line makes roughly a unit a minute, thus 6 * 480 ( the amount of minutes in a 8 hours) = 2880?

Edit: I know it's probably over 3000 as I think that each line is making 1.1 units.

Edited by danydandan
##### Share on other sites

6 hours ago, danydandan said:

Eh.

Around 2880?

Each line makes roughly a unit a minute, thus 6 * 480 ( the amount of minutes in a 8 hours) = 2880?

Edit: I know it's probably over 3000 as I think that each line is making 1.1 units.

I think you are misinterpreting the phrase 'any 5 of its production lines can manufacture 200 laser printers in 3 hours'. This is not 'any one of the 5' but 'any combination of 5'.

I told RabidMongoose I would put the solution up tomorrow if it is not posted before then.

##### Share on other sites

22 minutes ago, Ozymandias said:

I think you are misinterpreting the phrase 'any 5 of its production lines can manufacture 200 laser printers in 3 hours'. This is not 'any one of the 5' but 'any combination of 5'.

I told RabidMongoose I would put the solution up tomorrow if it is not posted before then.

Ah. Ok, I also completely didn't read the part where you say ratio and proportion in the intro.

I'll try again in a sec.

@Ozymandias. It isn't 640 is it.

Edited by danydandan
• 1
##### Share on other sites

On 11/03/2019 at 8:31 PM, danydandan said:

It isn't 640 is it.

It sure is, Dan. 640 is the correct answer and here is the solution:

5 lines produce 200 laser printers in 3 hours.

1 line produces 200÷5 printers in 3 hours.

1 line produces (200÷5)÷3 printers in 1 hour.

6 lines produce [(200÷5)÷3]×6 printers in 1 hour.

6 lines produce [(200÷5)÷3]×6×8 printers in 8 hours.

[(200÷5)÷3]×6×8 = 640 laser printers in total.

Are you going to set another teaser?

##### Share on other sites

8 hours ago, Ozymandias said:

It sure is, Dan. 640 is the correct answer and here is the solution:

5 lines produce 200 laser printers in 3 hours.

1 line produces 200÷5 printers in 3 hours.

1 line produces (200÷5)÷3 printers in 1 hour.

6 lines produce [(200÷5)÷3]×6 printers in 1 hour.

6 lines produce [(200÷5)÷3]×6×8 printers in 8 hours.

[(200÷5)÷3]×6×8 = 640 laser printers in total.

Are you going to set another teaser?

Yeap I'll set one in the same vein.

Theresa May has 650 possible votes for her Brexit plan, 391 of which are Nay and 242 of which are Yea. In a make believe scenario, Jeremy Corbyn went to the EU behind Mays back and secured his own deal. His Brexit plan has a possible 480 votes, all of them either Yea or Nay. If the ratio of Yea to Nay is the same for both May and Corbyn, then May has how many more Nay's than Corbyn?

Edited by danydandan
##### Share on other sites

15 hours ago, danydandan said:

Yeap I'll set one in the same vein.

Theresa May has 650 possible votes for her Brexit plan, 391 of which are Nay and 242 of which are Yea. In a make believe scenario, Jeremy Corbyn went to the EU behind Mays back and secured his own deal. His Brexit plan has a possible 480 votes, all of them either Yea or Nay. If the ratio of Yea to Nay is the same for both May and Corbyn, then May has how many more Nay's than Corbyn?

These figures result in decimal fractions, not whole numbers.

May's ratio of Yea to Nay is 242 : 391.

Divide Corbyn's 480 votes in the same ratio:-

480 × (242/633) = 183.51 Yea

480 × (391/633) = 296.49 Nay

May's Nays less Corbyn's Nays is 391 - 296.49 = 94.51

• 1
##### Share on other sites

12 hours ago, Ozymandias said:

These figures result in decimal fractions, not whole numbers.

May's ratio of Yea to Nay is 242 : 391.

Divide Corbyn's 480 votes in the same ratio:-

480 × (242/633) = 183.51 Yea

480 × (391/633) = 296.49 Nay

May's Nays less Corbyn's Nays is 391 - 296.49 = 94.51

Yeap. I thought the relevance of Brexit might interest some people in participating.

Your go to set a question.

Edit: I initially just did the arithmetic in my head, then realised before it was too late that it wasn't whole number conclusion.

Edited by danydandan
##### Share on other sites

Numbers in a sequence are generated by multiplying successive terms by the same factor. The first four numbers are

24,   X,   Y,   375

What is X and Y?