Answer:
The weight of 12 tennis balls = 691. 2 grams
Step-by-step explanation:
The weight of each tennis ball = 57.6 grams
So, the weight of 12 balls = 12 x ( weight of 1 ball)
= 12 x 57.6 grams
= 691.2 grams
⇒12 balls weigh 691.2 grams
Hence, the weight of 12 tennis balls = 691. 2 grams
A and B must be disjoint. You have, by the inclusion/exclusion principle, that

where the last term is required to prevent double counting. When

and

are disjoint, you have

and

, leaving you with
Answer:
18 kmh
Step-by-step explanation:
Given: Speed of cyclist is 9 km/h more than skater´s speed.
Distance covered at the given time by cyclist is 45 km and by skater is 30 km.
Let´s assume the speed of skater be "x"
∴ Speed of cyclist will be 
Remember; time= 
We know the time taken by both cyclist and skater are same.
∴ we can form an equation to find the speed of skater.
Time taken by cyclist= time taken by skater
⇒ 
Multiplying both side by 
⇒ 
Using distributive property of multiplication
⇒
Subtracting both side by 30x
⇒
Dividing both side by 15
⇒
∴
Hence, speed of the skater is 18 kmh