What is the value of a 1950 A US 20 dollar bill?

As of 02/2011, average-condition 1950 US $20 bills with no series letter, or an A, B, C, or D next to the date are worth about $24. Nice uncirculated ones could sell for $35 or so.

In God We Trust

That motto wasn't added to US bills until the late 1950s and early 1960s, so it's perfectly normal for it to be missing from 1950-series bills.

Serial Numbers

A bill's serial number is a counter and a security feature. In most cases it doesn't affect a bill's value or help to identify it.

DISCLAIMER: The values quoted are market averages as of the date shown, but may be different for an individual bill due to variations in quality and other factors. Also the wholesale (buying) price of a bill will be less than the selling (retail) price. A reputable currency dealer will be able to give a more accurate valuation based on an in-person inspection.