Since Annie needs 5 pencils, Brandon needs 8 pencils and Clara needs 13 pencils, the total number of pencils they need between them is 5 + 8 + 13 = 26. However, pencils only come in packs of 10, which means they need to round up the number of pencils they need to the nearest 10, which is 30. 30 divided by 10 gives you 3, which means Annie, Brandon and Clara need to buy 3 packs of pencils between them.