Using long and short strums is a handy way of getting used to a triplet rhythm. A long strum is a normal down-strum. striking across all or most of the strings. Using a short strum only requires the right hand to strum the middle two or three strings of the guitar. The photos below show approximately which strings are strummed using long and short strums.
Applying this principal to a triplet rhythm will help achieve the correct "feel" for triplet rhythm. A long strum is used on every beat and a short sturm is used on the "and" and "ahs". Long and short strums are illustrated by the use of a long arrow and a short arrow as shown below.
B7
Three O’Clock Blues is an eight bar blues progression with a distinctive "blues" sound. The triplet rhythm shown in Example 25 is played throughout the progression. The symbol C means repeat the previous rhythm patterns. The new chord B7 will also be used.