A7. Anne and Bob are in a fairground attraction. They move in circles around the same center and in the same direction. Anne goes around once every 20 seconds, Bob once every 28 seconds. At a given moment, they are at the smallest possible distance from each other (see the drawing).

How many seconds will it take for Anne and Bob to be at the greatest possible distance from each other?

![](https://cdn.mathpix.com/cropped/2024_04_17_a91c336121b9423a3a1eg-2.jpg?height=308&width=374&top_left_y=717&top_left_x=1521)
A) 22.5
B) 35
C) 40
D) 49
E) 70
A7. C) 35 In 140 seconds, Anne has completed 7 laps and Bob 5. At that moment, Anne's lead is two whole laps. $\mathrm{After} \frac{140}{4}=35$ seconds, Anne is half a lap ahead. This is exactly the first time she is as far away from Bob as possible.