There are two problems relating to Elon Musk. Solve either one for credit; solve both for extra credit!
Many thanks to Kate Neill and Ray Frantz for their ideas for these problems.
(1) With Donald Trump's return to the White House and his campaign promises to cut regulations and lower taxes, many anticipated that 2025 would be a banner year for billionaires.
However, market volatility in the wake of new tariffs and mounting concerns over a U.S. recession have created uncertainty in the U.S. economy.
As of Monday, March 10, 2025 the world's richest person, Elon Musk, had lost $132 billion this calendar year and now has a net worth of $301 billion.
But not to worry. Even with a net worth of "only" $301 billion left, Musk should be able to live comfortably for the rest of his life. How well?
Let's calculate.
As of 11 March 2025, Musk was 53 years old. He was born on 28 June 1971. If Musk lives to his biblical "three-score-and-ten" (i.e., 70 years) and dies on his birthday at age 70,
how much of his net worth would Musk have to spend each day from 11 March 2025 until his death in order to have no net worth when he died?
Don't forget to calculate leap years!
(2) On January 21, 2025, Tesla stock was trading at $424.07 on the stock market. One month later, on February 21, Tesla stock had fallen to $337.80.
If the stock continued to fall at the same monthly percentage rate, in what month and year would the Tesla stock be worth less than a dollar?
In the problem, the stock would be worth $269.08 on March 21, 2025 -- this is a check to see if you are doing the problem correctly
(FYI: the actual value of Tesla stock on March 10 was $222.15 but this has nothing to do with the problem).
Solution to the Problem:
Here are the solutions:(1) Elon Musk would have to spend $50,554,249.24 each day from March 11, 2025 to June 28, 2041 to have no net worth.
First, you must calculate the number of days from March 11,2025 to June 28, 2041 (when Musk turns 70 years old).
Hear are the number of days for each year:
| Year | # of Days |
|---|---|
| 2025 | 296 |
| 2026 | 365 |
| 2027 | 365 |
| 2028 | 366 |
| 2029 | 365 |
| 2030 | 365 |
| 2031 | 365 |
| 2032 | 366 |
| 2033 | 365 |
| 2034 | 365 |
| 2035 | 365 |
| 2036 | 366 |
| 2037 | 365 |
| 2038 | 365 |
| 2039 | 365 |
| 2040 | 366 |
| 2041 | 179 |
So, the total number of days from March 11, 2025 to June 28, 2041 is 5,954.
Divide $301,000,000,000 by 5,954 to get $50,554,249.24.
So, Elon Musk would have to spend over $50 million each day from March 11, 2025 until his 70th birthday on June 28, 2041 to have no net worth.
(2) On April 21, 2027, Tesla stock would be worth 91 cents, so it would take 27 months for the stock price to fall below a dollar.
This is a geometric sequence, so you must first determine the common ratio. The initial value, a1 = $424.07 and the second value, a2 = $337.80.
So r = 337.80 / 424.07 = .79656660457.
You can use the formula for a geometric sequence to determine the value of any term: xn = a1 rn - 1.
Here is a table of the projected prices for Tesla stock:
| Date | Value |
|---|---|
| Jan 21, 2025 | $424.07 |
| Feb 21, 2025 | $337.80 |
| Mar 21, 2025 | $269.08 |
| Apr 21, 2025 | $214.34 |
| May 21, 2025 | $170.73 |
| Jun 21, 2025 | $136.60 |
| Jul 21, 2025 | $108.33 |
| Aug 21, 2025 | $86.29 |
| Sep 21, 2025 | $68.74 |
| Oct 21, 2025 | $54.75 |
| Nov 21, 2025 | $43.61 |
| Dec 21, 2025 | $34.74 |
| Jan 21, 2026 | $27.67 |
| Feb 21, 2026 | $22.04 |
| Mar 21, 2026 | $17.56 |
| Apr 21, 2026 | $13.99 |
| May 21, 2026 | $11.14 |
| Jun 21, 2026 | $8.88 |
| Jul 21, 2026 | $7.07 |
| Aug 21, 2026 | $5.63 |
| Sep 21, 2026 | $4.49 |
| Oct 21, 2026 | $3.57 |
| Nov 21, 2026 | $2.85 |
| Dec 21, 2026 | $2.26 |
| Jan 21, 2027 | $1.81 |
| Feb 21, 2027 | $1.43 |
| Mar 21, 2027 | $1.14 |
| Apr 21, 2027 | $0.91 |
Correctly solved by:
| 1. Colin (Yowie) Bowey ** | Beechworth, Victoria, Australia |
| 2. Davit Banana ** | Istanbul, Turkey |
** Extra credit for solving both problems