PSLE
Gabriel packed 438 wafers into large and small boxes. He filled each large box with 18 wafers and each small box with 6 wafers. All the boxes were full and no wafers were left over. What was the least number of boxes used by Gabriel?
To have the least number of boxes, Gabriel had to use as many as large boxes as possible.

If Gabriel used only large boxes,
number of large boxes used
= 438 ÷ 18
= 24 r 6 (x) There should be no remaining wafers left.

If 24 large boxes are used, there are 6 wafers left, Gabriel had to use less large boxes so that the rest of the wafers were packed in small boxes.

If Gabriel used 23 large boxes,
number of wafers to be packed in small boxes
= 438 - (23 x 18)
= 438 - 414
= 24

Number of small boxes needed to pack 24 wafers
= 24 ÷ 6
= 4 (✓) There is no remaining wafers left.

Least number of boxes that Gabriel used
= 23 + 4
= 27

Answer(s): 27