you go to the grocery store every 4 days. your friend goes to the grocery store every 10 days. if you both go to the store today, when will you both go to the grocery store again on the same day.
every 20 days because you go every 4 days so when you go on your fith round of those 4 days it would be your friends 2nd time shopping in your Friends 10 shopping daysÂ