Question

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You go to the grocery store every 4 days. Your friend goes to the grocery store every 10 days. If you and your friend both go to the grocery store today, when will you both go to the grocery store again on the same day?


in 10 days


in 20 days


in 16 days


in 40 days

Answer 1

You need to find the LCM of 4 and 10

So if you go every 4 days
you're going on day 4, 8, 12, ...

just count by 4

and if your friend goes every 10 days,
he is going on day 10, 20, 30...

just count by 10

can you continue the counting for 4

4, 8, 12, 16, ...

Answer 2

we want to find the smallest number that's common to both of them