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# math problem sum

+1
274
3

two crickets croak every 15 minutes and 20 minutes. given that they croaked at the same time 12pm, at what time would they would croak at the same time again

Guest Nov 23, 2015

#1
+10

15=3 X 5

20=2 X 2 X 5

LCM=3 X 2 X 2 X5=60

The two crickets will chirp again together in 60 minutes or in one hour from 12pm, which will be at 1:00pm.

Guest Nov 23, 2015
Sort:

#1
+10

15=3 X 5

20=2 X 2 X 5

LCM=3 X 2 X 2 X5=60

The two crickets will chirp again together in 60 minutes or in one hour from 12pm, which will be at 1:00pm.

Guest Nov 23, 2015
#2
+91039
0

Thanks you guest. :)

This question is trivial but I am wondering how you would set up and solve a more difficult question like this using modular arithmetic  ??

Melody  Nov 23, 2015
#3
0

With SMALL numbers another way this can be done is to list the first few multiples of each number to see when(if) they match

example    every 15 mins      15   30  45  60  75

every 20 mins      20   40  60   80              You can quickly see 60 is the first match, so the answer would be 60 minutes after 12pm ...or  1 pm

Guest Nov 23, 2015

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