It's been a historic and exceptionally volatile past couple of trading sessions for the stock market.

It began with the descent of all three major U.S. indexes -- the Dow Jones Industrial Average, Nasdaq Composite, and broad-based S&P 500 -- into correction territory faster than any previous correction. Going from an all-time high on the S&P 500 to official correction territory -- that's a decline of 10%, not rounded -- took just eight calendar days and six trading sessions.

Additionally, we've seen all three major indexes log their biggest point declines in history on Thursday, Feb. 27, only to turn around and record their largest point increases in history this past Monday, March 2.

Knowing full well that stock market corrections have historically been an excellent time to put money to work, I wound up adding to or opening a position in six stocks last week. While two of them are too small for me to discuss here at the Fool (they're under $200 million in market cap), I will outline my thinking as to why I bought the following four stocks as the market "plunged."

A stopwatch with the words, Time to Buy, written on the dial.

Image source: Getty Images.

Pinterest

I've been threatening to do it for months, but I finally got the nerve to dip my toes into the pond last week by opening a position in social media company Pinterest (NYSE:PINS).

Following the release of Pinterest's fourth-quarter and full-year results in early February, what stood out is the steady success the company is having in attracting international users. It's never been a secret that average revenue per user (ARPU) -- Pinterest primarily generates revenue through ads -- is substantially higher in the United States relative to international markets, but there's a much broader audience and a greater potential for ARPU growth overseas. During the fourth quarter, international ARPU grew to $0.22 per user, representing an improvement of 122%. U.S. ARPU was up 26%, as well. This demonstrates that Pinterest's pull with advertisers is growing, as is its monthly active user count (335 million in Q4 2019, versus 265 million in Q4 2018). 

Just as important, after growing sales by 51% in 2019, Pinterest is looking to keep momentum going, with projected sales growth of 33%. This should be enough to push Pinterest toward recurring profitability sometime in 2020.

With Pinterest beginning to connect the dots between member interests and e-commerce, and its emphasis of video, which leads to improved member engagement, I'm very excited to see what the future holds for the company.

A woman using a device to check her blood glucose levels.

Image source: Livongo Health.

Livongo Health

Speaking of companies that truly excite me, there's health-solutions provider Livongo Health (NASDAQ:LVGO), which I opened a position in last week during the market meltdown.

The thesis here is pretty simple. There are more than 34 million people in the U.S. with diabetes (that's 10.5% of the population), and 88 million additional adults that have prediabetes, which can lead to diabetes if left untreated. Diabetes (along with its numerous co-morbidities) is one of the leading causes of death in the U.S., and a lack of action on the part of diabetics is a big reason this disease is such a killer. After watching other diabetes stocks soar throughout the years, Livongo Health and its new way of approaching the treatment process stood out from the crowd. 

Utilizing a suite of wirelessly connected devices, Livongo Health aims to change the behavioral habits of diabetics to ensure they take better care of themselves, leading to improved patient outcomes. In 2019, member count nearly doubled (up 96%) to 222,700 members, with client count (i.e., enterprises using Livongo's health solutions) up 95% to 804. Perhaps more impressive, Livongo managed to generate positive adjusted EBITDA during the fourth quarter, showing that it's already making the turn toward recurring profitability despite heavy reinvestment. 

With the understanding that diabetes will remain a serious problem within the U.S. and globally for the foreseeable future, I view Livongo Health's addressable market as massive and believe it's an incredible bargain.

An engineer inspecting a gas turbine outside of a power plant.

Image source: Getty Images.

Fluor

I'm a firm believer that every investors needs a feel-good story and/or dart-throw investment from time to time. For me, that's engineering, construction, and consulting company Fluor (NYSE:FLR), which I owned a stake in before last week's stock market "plunge," but I added to it during the week.

Fluor was nothing short of a disaster in February, mostly because the company delayed its 10-K filing and announced an accounting probe from the Securities and Exchange Commission (SEC). Generally, accounting probes would put a company off limits for me as an investor. However, the probe itself simply concerns how the company recorded charges during the second quarter, which, in my view, won't make a significant difference even if deficiencies are found. While it'd be a knock against Fluor's corporate oversight, this particular SEC probe holds virtually no weight related to the company's operating performance.

What we did get from the company was an unaudited update on key metrics. Fluor ended 2019 with $32.7 billion in backlogged projects after being awarded $12.6 billion in projects throughout the year. This represents more than a 1.5 years of revenue waiting in the wings. 

The company also projected $1.40 to $1.60 in full-year adjusted earnings per share, albeit provided no sales forecast. At the midpoint, Fluor is valued at less than seven times this year's EPS forecast. That's roughly half of the average forward P/E Fluor has traded at over the past five years. The company is also valued at only five times its cash flow, which is at least a decade low. I believe investors who are willing to give Fluor a good three-to-five years to recover will be more than pleasantly surprised with the outcome.

An offshore oil-drilling platform.

Image source: Getty Images.

ExxonMobil

The fourth top stock I gobbled up the stock market screamed lower was integrated oil and gas giant ExxonMobil (NYSE:XOM).

Despite being snake-bitten by oil drilling and exploration companies in the past, I simply couldn't turn down the opportunity to own such a diversified energy company that was, at the time, trading at a 16-year low.

Although ExxonMobil may face near-term challenges, especially with the winds of recession blowing in the wake of the coronavirus disease 2019 scare, its business is hedged perfectly to continue generating significant cash flow even with West Texas Intermediate crude below $50 a barrel. While drilling and exploration is its bread and butter, ExxonMobil is able to offset crude's weakness by upticks in demand at the refining and petrochemical level.

Speaking of cash flow, ExxonMobil's price-to-cash-flow ratio was down to as low as 7 last week, which would be its lowest level since 2012 and close to 40% below its average valuation multiple relative to cash flow over the past five years. With the understanding that ExxonMobil is better positioned to handle low crude prices than many of its peers, this low price-to-cash-flow figure suggests there's real value to be had for patient investors.

Lastly, it's hard to go wrong when choosing a Dividend Aristocrat. ExxonMobil has raised its payout an incredible 37 consecutive years and is currently yielding 6.5%, which is roughly triple the yield of the S&P 500. That's a relatively safe yield you'll find is hard to top.