Alex runs up a staircase with n steps, and can hop either 1, 2, or 3 steps at a time. count how many possible ways the child can run up the stairs. solution?

There are 4 possible ways

Step-by-step explanation:

Data provided in the question:

Alex can hop in 1 steps, 2 steps, or 3 steps at a time.

From the above data it can be concluded that at a single maximum 3 steps can be run at a time

thus,

for running 3 steps at a time from the above data, we can have

with 1 step only : {1 , 1 , 1}

with 1 step first and 2 steps : {1 , 2}

with 2 steps first and then the 1 step: {2 , 1}

and 3 steps at once : {3}

thus, we have 4 possible ways to run up the stairs keeping the above condition.

0.00067=67X10^5 so

67X10^5-2.3X10^5

64.7X10^5 which can be expressed as:

6.47X10^6

(not sure if it matters to you or not, but technically we only had two significant figures so it should be rounded to 6.5X10^6)