If in the medium both glucose and lactose are present in same concentration, then:

If bacterial cells are supplied with glucose as well as a variety of other substrates, such as lactose or galactose, the cells catabolize the glucose first and ignore the other sugars. The glucose in the medium acts to repress the production of various catabolic enzymes, such as β ‐galactosidase, that would allow utilization of the other sugars.