Question

SAT Help

Answer 1

Answer:

In 7*5 = 35 days, Jack can paint 7 houses.

In 5*7 = 35 days, Richard can paint 5 houses.

So in 35 days, the two of them can paint 12 houses. To paint just one house, they'll need 1/12 the time, or 35/12 = 2 11/12 days.

Step-by-step explanation:

Answer 2

Well, their speeds are ($V_1$ is Jack's speed, and $V_2$ is Richard's.
$V_1 = \frac{1}{5} houses/day \\ V_2 = \frac{1}{7} houses/day \\ V = V_1 + V_2 = \frac{1}{5}+\frac{1}{7} = \frac{7+5}{35} = \frac{12}{35}$
They, together, can paint 12 houses in 35 days. To get a single house, we only have to calculate $\frac{35}{12}$ which is very close to 3 (a bit below)