PSLE
David packed 396 biscuits into large and small boxes. He filled each large box with 14 biscuits and each small box with 6 biscuits. All the boxes were full and no biscuits were left over. What was the least number of boxes used by David?
To have the least number of boxes, David had to use as many as large boxes as possible.

If David used only large boxes,
number of large boxes used
= 396 ÷ 14
= 28 r 4 (x) There should be no remaining biscuits left.

If 28 large boxes are used, there are 4 biscuits left, David had to use less large boxes so that the rest of the biscuits were packed in small boxes.

If David used 27 large boxes,
number of biscuits to be packed in small boxes
= 396 - (27 x 14)
= 396 - 378
= 18

Number of small boxes needed to pack 18 biscuits
= 18 ÷ 6
= 3 (✓) There is no remaining biscuits left.

Least number of boxes that David used
= 27 + 3
= 30

Answer(s): 30