What single decimal multiplier would you use to increase by 5% followed by a 20% increase?

The desired single multiplier is 1.26.

Step-by-step explanation:

A 5% increase results in the original amount PLUS 5% of the original amount:

1.05(original amount)

If a 20% increase follows, we must multiply the above 1.05(original amount) by 1.20:

1.20(1.05)(original amount), or (after multiplying), 1.26.

The desired single multiplier is 1.26.