Diaries are sold in a box of 12
Pencil are sold in a box of 10
Ruler are sold in a box of 6
The teacher need to buy all the items in same amount.
So we have to find out here LCM of 3 numbers.
LCM of 12,10 and 6 is 60.
So number of Diaries box to buy=60/12 =5 boxes
Number of pencils are to be bought=60/10 = 6 boxes
Number of ruler to be bought=60/6=10 boxes. (Answer)