Should you buy last week’s losers Legal & General Group plc (-9%), Cobham plc (-28%) and St Ives plc (-50%)?

Today I’m considering the investment case for three FTSE-quoted fallers.

A financial firecracker

Insurance goliath Legal & General’s (LSE: LGEN) share price suffered a mild hiccup last week, a 9% decline taking it to levels not seen since late February.

I see this weakness as a fresh buying opportunity, however, and expect the firm to regain its upward momentum sooner rather than later.

The company’s tearaway success around the globe continues to deliver terrific returns, and total assets under management leapt 8% in 2015 to £746.1bn. And I believe new business generation should keep on surging as Legal & General expands its presence in the US and Asia in particular.

Indeed, the City expects Legal & General to enjoy earnings rises of 8% and 7% in 2016 and 2017, respectively, figures that make the insurer appear chronically undervalued — the company carries P/E ratings of just 10.9 times and 10.1 times for these years. I reckon the company is a savvy bargain buy at current prices.

Defence play dives

Defence giant Cobham (LSE: COB) sent shockwaves across markets last week after releasing hugely-disappointing trading numbers.

The engineering play shed a quarter of its share value after announcing that a variety of operational problems forced first-quarter profit to slump to £15m from £50m in the same 2015 period. As a consequence Cobham now expects full-year trading profit to clock in £15m lower than the previous estimate of £315m.

As if this wasn’t enough, Cobham advised that it would need to raise £500m via an emergency rights issue. The cost of borrowings to fund its Aeroflex acquisition in 2014 hadn’t fallen as quickly as hoped, it said, putting it in danger of breaching loan covenants.

The City expects Cobham to endure a 12% earnings slide in 2016, resulting in an ultra-low P/E rating of 8.7 times. Still, I reckon the scale of problems across its core markets and its fragile balance sheet make the business a risk too far even at current prices.

Profits sinking

But Cobham wasn’t the only Footsie firm to collapse last week, the engineer’s slide was put in the shade by St Ives (LSE: SIV) whose share price more than halved from Monday to Friday.

The marketing services play tanked after advising that “underlying profit before tax for the current financial year is likely to be materially below management’s current expectations” thanks to deteriorating conditions in the final quarter. Indeed, St Ives noted that global economic uncertainty “has led to the cancellation and deferral of a number of significant projects.”

Rubbing salt in the wounds, St Ives added that “while it is too early to judge with accuracy at this stage, it is expected that these factors will impact the outturn for the next financial year also.”

The number crunchers expect St Ives to endure a 5% earnings slip in the year to July 2016, resulting in a P/E rating of just 5.8 times. However, I reckon value seekers should steer well clear, as escalating jitters over the health of the global economy could prompt further problems over at St Ives.

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Royston Wild has no position in any shares mentioned. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.