Two fifths, one-third and three eighties are arranged from small to large

Two fifths, one-third and three eighties are arranged from small to large

2/5=48/120
1/3=40/120
3/8=45/120
40/120

A Mathematical Olympiad in primary school
There is an electronic clock, which lights up every 9 minutes, rings every hour, and lights up at 12 o'clock. The next time it rings and lights up is () o'clock
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I think there is a decimal system in this problem, but I don't know what it is. In this way, I will understand

Since the electronic clock rings on the hour, we only need to consider which time to turn on the light. From 12 noon, how many 9 minutes does it take to turn on the light every 9 minutes? Since 1 hour = 60 minutes, the problem is: how many times of 9 minutes is the integral multiple of 6O minutes? In this way, the essence of the problem is clear: the least common multiple of 9 minutes and 60 minutes
It is not difficult to calculate that the least common multiple of 9 and 60 is 180. That is to say, 180 minutes from noon, that is, three hours, the electronic clock will ring and light up again
A: the next time the bell rings and the light goes on is at 3pm

Mathematical Olympiad in primary school: (1 + 2 / 5) × (1-2 / 5) × (1 + 2 / 7) × (1-2 / 7) × ×(1+2/2005) ×(1-2/2005)

(2007/5) ×(3/2005) (7/5)x(3/5)x(9/7)x(5/7)x...x(2007/5)x(2003/2005)=[(7/5)x(9/7)x.X(2007/5)]x[(3/5)x(5/7)x...x(2003/2005)]=(2007/5)x(3/2005)=6021/10025