One minute later at 8:01pm. One lighthouse will flash 3 times (at 20, 40 and 60 seconds)...the other will flash twice (at 30 and 60 seconds). So they will both flash 60 seconds later, at 8:01
Answer
215 can only be divided by 5
For this case, the first thing we must do is define variables.
We have then:
x: number of pens
y: number of pencils
We now write the system of inequations:

The solution to the system of inequations is given by the shaded region.
Note: see attached image.
Answer:
c=13
Step-by-step explanation:
c-8=5
Add 8 to each side
c-8+8 = 5+8
c=13