Algebra

Let's find the rate for each person. You can do this by using the formula "work = (rate)(time)(number of people). Plugging in we get: 

$1000 = r(10)(10)$

$\frac{1000}{100}=r$

$r = 10$

Now we can use the rate to find out the time in the second equation.

$1000 = 10(t)(5)$

$\frac{1000}{50} = t$

$\mathbf{t = 20}$

Therefore, it would take 20 minutes for 5 members to paint a 1000 square foot wall.