PSLE
Henry packed 482 wafers into large and small boxes. He filled each large box with 18 wafers and each small box with 10 wafers. All the boxes were full and no wafers were left over. What was the least number of boxes used by Henry?
To have the least number of boxes, Henry had to use as many as large boxes as possible.

If Henry used only large boxes,
number of large boxes used
= 482 ÷ 18
= 26 r 14 (x) There should be no remaining wafers left.

If 26 large boxes are used, there are 14 wafers left, Henry had to use less large boxes so that the rest of the wafers were packed in small boxes.

If Henry used 25 large boxes,
number of wafers to be packed in small boxes
= 482 - (25 x 18)
= 482 - 450
= 32

Number of small boxes needed to pack 32 wafers
= 32 ÷ 10
= 3 r 2 (x)

There should be no remaining wafers left. So, Henry had to use less large boxes.

If Henry used 24 large boxes,
number of wafers to be packed in small boxes
= 482 - (24 x 18)
= 482 - 432
= 50

Number of small boxes to pack 50 wafers
= 50 ÷ 10
= 5 r 0 (✓) There is no remaining wafers left.

Least number of boxes that Henry used
= 24 + 5
= 29

Answer(s): 29