In a sample of 77 children, the mean age as at which they first began to combine words was 16.51 months

Mean age = 1271.27

Step-by-step explanation:

No of children = 77

The age at which children first began to combine words = 16.51 months

Mean age = No of children * age at which children first began to combine words

= 77 * 16.51

= 1271.27

Mean age = 1271.27