## What Makes Us Successful

January 5, 2021 Leave a comment

Math and Logic Puzzles

January 5, 2021 Leave a comment

December 7, 2020 Leave a comment

Being a brainaire makes you feel probably better than just being a billionaire, isn’t it?

You can earn billions brain coins at Brainaire website that is full of logic brainteasers and funny questions. It is free and everything depends on your intelligence and your persistence. Give it a try at www.aplusclick.org/brain/ . You will not regret.

This is a sample question for a Brainiare:

What is the largest of the four options?

M L XL X

October 4, 2020 Leave a comment

Real examples help to better understand how to interpret the statistics.

**False Positive Paradox**: A particular medical test for a disease is 96% accurate. If one has the disease, the test comes back ‘Yes’ 96% of the time, and if one does not have the disease, the test comes back ‘Yes’ 4% of the time.

If 100 of 10000 tested patients have the disease, what is the probability that the person with the diagnosis ‘Yes’ has the disease?

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**Effective Average Infection Ratio**: R is the effective average infection ratio for a disease, also known as the reproduction number. It is the average number of secondary infections caused by one person. (Infections caused by the secondary infections – which would be tertiary infections – are not counted). Consider 50 infected people. Suppose 49 spread the infection to nobody, but one person spreads the infection to 60 people.

What is the R-value?

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*Leslie Green* asks: How would you propose **to deal with the COVID-19 **pandemic, given information current at the time of writing (11 October 2020).

A. Severe lockdown for 4 weeks

B. Ignore it and carry on as normal

C. Partial lockdown and wait for a vaccine

D. Some other idea

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The Pfizer COVID-19 vaccine-candidate interim results from 8 Nov 2020 showed 38,955 participants in a placebo controlled double-blind trial.

94 participants became “evaluable”, which we presume to mean they showed COVID-19 symptoms. The analysis presented was that the **vaccine efficacy rate** was above 90%. What is the maximum number of (genuinely) vaccinated people who showed COVID-19 symptoms?

Variability Analysis on COVID-19 Interim Trial Data by *Leslie Green*

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Is there any rational justification for being wary of **vaccines**?

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In the UK, December 2020, up to 2 million university students were potentially going home for Xmas during the middle of the COVID-19 pandemic. A new fast COVID-19 test had been developed to spot the causative virus, SARS-CoV-2. These *lateral flow tests* had the characteristics shown in the image. At the time, around 1% of the population had the virus within the community.

The scientific advice, given on prime-time news channels, was that a pair of negative tests meant it was safe to go home, as a negative test meant a 99.75% chance of not having the virus.

Was this true, and good advice?

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May 9, 2020 Leave a comment

You are buying a roller on Amazon. Four similar rollers have the same functions, the same price, the same look, but different ratings.

Which product do you choose?

A. 8 positive ratings (8 total ratings)

B. 45 positive ratings (48 total ratings)

C. 90 positive ratings (98 total ratings)

D. 177 positive ratings (198 total ratings)

Find the answer at aplusclick.org.

April 5, 2020 Leave a comment

There are 5 counters in a bag. Three are Argentinean (blue) and two are Brazilian (green). Three counters are randomly picked out of the bag, one by one. They are not returned to the bag.

What probability is higher?

A. The probability of choosing * three Argentinean counters* in a row.

B. The probability of choosing * two Brazilian counters* in a row and then one Argentinean counter.

Find the answer.

March 1, 2020 Leave a comment

There was a tradition in old Russia. A would-be bride gathers six long pieces of straw and grasp them in her hand. She then randomly ties pairs of knots on the top and the bottom. Since there are six blades of grass sticking out above and below the hand, she will tie three knots on the top and three knots on the bottom. If she forms one big ring, she gets married soon.

Estimate the probability that the girl will get married soon.

*The problem is mentioned in The New York Times NUMBERPLAY and it is credited to Sunil Singh.*

February 16, 2020 Leave a comment

Seven secret agents are on payroll of a government.

Secret agent 001 spies on a secret agent who spies on secret agent 002,

who spies on a secret agent who spies on secret agent 003,

who spies on . . . spies on secret agent 007

who spies on a secret agent who spies on secret agent 001.

Who spies on secret agent 007?

January 13, 2020 Leave a comment

Gerry has several pets at home.

All of them are dogs, except for three.

All of them are cats, except for four.

All of them are tortoises, except for five.

How many dogs does he have?

December 1, 2019 Leave a comment

These are the Best Puzzles published at www.aplusclick.org in 2019.