Flashing lights

Question

Light A turns on every other second.
Light B turns on every other second and stays on for another 1s.
Light C turns on every other second and stays on for another 3s.

Light A is off.
Light B is off.
Light C has been on for 4s.

In how many seconds will all of the lights be on at the same time?

Answer 1

Each row is one second of time...

1 is on, 0 is off

A B C

0 0 1 <-- time zero

1 1 0

0 1 1

1 0 1

0 1 1

1 1 0

0 0 1

1 1 1 <--

0 1 1

7 seconds