An infant's pulse rate is measured to be 127 ± 4 beats/min. what are the uncertainty and the percent uncertainty in this measurement?

The uncertainty in a measured value is the possible variation in a measured value arising due to inaccuracies in the instrument being used. In the case described, the beats are 127 per minute, and the uncertainty is + / - 4 beats. This means that the beats may actually be between 123 and 131.

The fractional uncertainty is: 4/127 = 0.031

And the percentage uncertainty is: 4/127 * 100 = 3.1%