Gifted nerds should be able to handle their finances.

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Ahmed and Aisha have their eyes on a house in Silicon Valley. The house costs a half a million dollars, and they want to finance the entire purchase price. The available fixed interest rate is 6%. For a 15-year mortgage that’s about $4,200 per month.

That’s way too much for their budget. So they ask about payments for 30 years.

Typically, the longer a mortgage lasts, the higher the interest rate. However, their broker says that because business is slow, he can offer a 6% rate regardless of the mortgage term.

He does some calculations and announces that a 30 year fixed mortgage at 6% would be about $3000 per month.

This was still too much money for Ahmed and Aisha. So Ahmed asks, “How long of a mortgage period can we take so that our monthly payments are half that, about $1,500 per month?”

The broker scratches his head and enters some numbers on his computer and sighs.

“Sorry,” he says, “The minimum I can get your house payment down to is $2,500 per month.”

Ahmed is confused.

“I thought we could stretch out the payments as long as we wanted to.”

 The broker shrugged.

“A hundred years, a thousand years, what’s the difference?”

 So here’s this week’s Micro Softy: Has the broker broken his promise to extend mortgage payments over as long a period as possible? And why is the $2,500 per month the minimum he can get for Ahmed and Aisha?

H2 Now here’s the solution to Monday Microsofty 103:  The Achepocalypse-Now Virus

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Here’s last week’s puzzle: One percent of the population carries the Achepocalypse-Now Virus. Your test comes back positive — but with a 10% false positive rate. What is the actual chance that you’re infected?

Here’s the surprising answer: There’s only an 8.3% chance you are infected with the virus. Here are the details:

If 1% of the population is infected, then in a group of 10,000 people, 100 actually have the virus and 9,900 do not. If the test is 90% accurate, it correctly flags 90 of the 100 infected people. But among the 9,900 healthy people, a 10% false positive rate incorrectly flags 990 healthy people as positive. So if you test positive, you’re one of 1,080 positive results, but only 90 actually have the virus.

That means your chance of being infected is only about 90/1080 = 8.3%. Even though you tested positive, you’re probably okay.

H2 The Monday Microsofty is a weekly feature of Mind Matters News. Here are the links to all the puzzles and answers to date:

Monday Microsofty 103:  The Achepocalypse-Now virus. What effect do false positives have on the significance of test results? Also, the level of accuracy claimed by the newspaper in last week’s puzzle is an eye-opener in a way that was not, perhaps, intended.

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Monday Microsofty 102:  News is 80% accurate 90% of the time. But what does that really mean? For last week’s puzzle, what if Bob and Connie each had some assistance while walking?

Monday Microsofty 101: Speed is relative. When two people holding hands show different distances on their fitness trackers, what is going on? The simplest solution to last week’s question involves preventing a royal flush.

Monday Microsofty 100: How to win at poker all the time. Choose any hand you want and I will still win. But why? The solution to the puzzle about cutting the fan belt is to remember that there is only ever one side.

Monday Microsofty 99: Fan belt cutting technology. The world of geometry features some strange elements, even in everyday things. The answer to last week’s puzzle lies in determining how many sides a belt must have. You can find links and answers to Microsofties 92 through 99 here as well.

Monday Microsofty 92: When the nerd enters a room… Shaking hands is expected. Here’s a math question about the custom, to delight the true nerds among us. A hint for Microsofty 91: Where might Jimmy the Mooch have found some spare energy? You can find links and answers to Microsofties 91 through 87 here as well.

Monday Microsofty 87: Are you as good a detective as you think? Here’s a test from the world of codebreaking To solve last week’s puzzle, look up the definition of “calorie.” Are we using the word to mean the same thing? You can find links and answers to Microsofties 77 through 86 here as well.

Monday Microsofty 76: The Smoking Gun explains a computer scientist or engineer, a law enforcement officer often relies on abductive reasoning to crack a case, so with this in mind, you will have to crack last week’s puzzle. You can find links and answers to Microsofties 55 through 75 here as well.

Monday Microsofty 55: “It happens every spring.” Baseball, that is. Here’s a puzzle that takes in baseball’s summer. To solve last week’s puzzle, you don’t need to know the distance. Check the problem again for the number you do need to know. You can find links and answers here to Microsofties 51 through 54 as well.

Monday Microsofty 50: Cutting through the cornbread. How did Yuri Senior cut the cornbread into eight identical portions using only three straight cuts? You can guess the answer to Microsofty 49 if you try the test question yourself at home, using a small mirror. You can find links and answers here to Microsofties 46 through 49 as well.

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Monday Microsofty 45: Can Tony beat the fast-food curfew? An early curfew on fast food service motivated a boy to exercise more vigorously. But how fast was he pedalling? To solve Micro Softy 44, recall that Tony doesn’t need to take the individual pills each day, only the prescribed amount of each. You can find links and answers here to Micros Softies 41 through 44 as well.

Monday Microsofty 40: The fate of a false prophet. He wasn’t actually fired for being a false prophet but for something that his prophecy unintentionally revealed. The solution to Micro Softy 39 lies in considering an alternative possible meaning of a word commonly used in sports. You can find links and answers here to Micro Softies 30 through 39 as well.

Monday Microsofty 29: A funeral lament in four lines. The funeral director was puzzled by Dan’s description of his relationship to the deceased but there was no question that his grief was sincere You can find links and answers here to Microsofties 22 through 29 as well.

Monday Microsofty 21: Finding More of the Deadly Fentanyl Pills. You can find links and answers here to Microsofties 11 through 20 as well.

Monday Microsofty 11: What Happened to That Other Dollar? You can find links and answers here to the first ten Micro Softies. Have fun!