TSA 2021 Question 2

Practice Question Solving
1

Hi, couldhI,Hi, could someone help me with this question please. I though that A was the answer, but in fact is B.

2 -The fairy lights on a Christmas tree are in three colours, blue, green and silver. The blue lights flash every 5 seconds, the green lights flash every 8 seconds and the silver lights flash every 12 seconds. The lights have all just flashed at the same time.
How many times will they all flash at the same time in the next 45 minutes?

A 5
B 22
C 45
D 108
E 112

2

Hi!

I first found the lowest common multiple of 5, 8 and 12: 5 * 2³ * 3 =120
So the lights flash at the same time every 120s.
45min=2700s
2700/120=22,5
so in 45min they flash at the same time 22 times.

2 Likes
3

Thats clear! Thanks Juliette!