Let's set up an equation to solve this problem.
Let m represent the number of minutes it will take Grandma to remove 30 weeds.
We know that Grandma can remove 5 weeds per minute. So, in m minutes, she will remove a total of 5m weeds.
Since she started with 250 weeds and wants to end with 30 weeds, we can set up our equation:
250 - 5m = 30
Now, let's solve for m:
250 - 30 = 5m
220 = 5m
m = 220/5
m = 44
It will take Grandma 44 minutes to only have 30 weeds remaining in the garden.