Textbooks are stored on 2 shelves. Each shelf is 0.72m long and each textbook is 30mm wide. Can 50 textbooks be stored on these 2 shelves?

First off, we better convert the 30mm into m. Now, we know that in 1cm there are 10mm. So in 2cm, there are going to 20mm and in 3cm there are going to be 30mm. So each textbook is really 3cm thick. Now, hopefully you know that 1cm is 1/100 (one "one-hundredth") of a metre. We've got 3cms, so we're going to have 3/100 (three "one-hundredths") of a metre. As a decimal, this is 0.03m.

Next, we better calculate our total shelf space, which is 2 x 0.72m = 1.44m. We want to work out how many textbooks (of width 0.03m) we can squeeze into our 1.44m of shelf space. So we're going to divide 1.44 by 0.03, to work out how many "lots of" 0.03 we can squeeze into 1.44. 1.44/0.03 gives us 48. So we can fit 48 textbooks onto the two shelves.

Hence we can't fit 50 textbooks onto the two shelves!