There are 150 students in grade six.

The number of people participating in the sports activity group is 150× 2/5 = 60.

The number of participants in the calligraphy group is 60/4/3 = 45.

The percentage of participants in the calligraphy group to the total number of students in the whole grade is 45/ 150 = 3/ 10.

Comprehensive formula: 2/5 ÷ 4/3 = 2/5× 3/4 = 3/ 10.