EasyMathematicsHigh School (9–10)GeneralNumber Systems › Divisibility, HCF and LCMNumericalreal-life
On a road, one traffic light turns green every 40 seconds and another every 56 seconds.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On a road, one traffic light turns green every seconds and another every seconds. Both turn green together at . After how many seconds do they next turn green together, and at what time is that?
Need a reminder? The key ideaShow
The largest equal size that fits exactly into some amounts is their HCF. The first time things happen together again is the LCM of their times. With remainders, take them away first (HCF) or add one to the LCM. Euclid's method: gives HCF HCF.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Choose. Together again: the LCM of and .
Step 2. LCM. seconds.
Step 3. The time. , so at .
Answer: after seconds, at .
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