If it takes 3 days for 10 workers to finish building one house, how many days will it take 15 workers to finish four houses?

-- It takes 10 workers 3 days to build 1 house.
so
-- It takes 10 workers 1 day to build  1/3  of a house.
so
-- It takes 1 worker 1 day to build  1/30  of a house.

You got 15 workers and you need 4 houses ?

Well, as we just calculated . . .

-- It takes 1 worker 1 day to build  1/30  of a house.
so
-- It takes 15 workers 1 day to build  15/30 = 1/2  of a house.
so
-- It takes 15 workers 2 days to build 1 whole house.
so
-- It takes 15 workers  8 days  to build 4 houses.

Hello!

the answer is:

the answer is:

why?

to solve the problem, we need to remember the quotient of power property, it's defined by the following relation:

if we have a quotienf of powers that have the same base, we need to keep the same base and subtract the exponent of the denominator power to the exponent of the numerator power.

so, we are given the expression:

then, calculating we have:

hence, the answer is:

have a nice day!