Final answer:
Thien has to take a total of 432 steps to reach the 11th floor.
Step-by-step explanation:
To calculate the number of steps Thien has to take to reach the 11th floor, we need to find the total number of steps he climbs to reach the 3rd floor and then add the additional steps to reach the 11th floor.
Given that Thien climbs 48 steps to reach the 3rd floor, we can calculate the additional steps by subtracting the number of steps from the 3rd floor to the 11th floor.
Since each floor has the same number of steps, we can calculate the additional steps as follows:
Number of steps from the 3rd floor to the 11th floor = (11 - 3) x 48 = 8 x 48 = 384 steps.
Therefore, Thien has to take a total of 48 + 384 = 432 steps to reach the 11th floor.