The science department buys equipment shown microscopes every 5 years safety goggles every four years test tubes every two years they bought all three items this year in how many years will they have to buy all three items again

This question requires you to know the lowest common multiple (LCM) of 5, 4 and 2. there are a few ways to do that. in this case the LCM would be 20. this means that in 20 year the science department would buy all 3 equipment at the same time 

Cbecause they are equal so that means it is the same on both sides? ! hope this