Reading the histogram, there was 1 student who took about 10 minutes and 2 students who took between 30 and 40 minutes to complete the test. The total number of students is 1 + 2 + 1 + 3 + 10 + 12 = 29, so 10% of 29 ~ 3. So, about (3 = 1 + 2 ~) 10% of students took less than 40 minutes to complete the test.