PSLE
Howard packed 392 tarts into large and small boxes. He filled each large box with 18 tarts and each small box with 10 tarts. All the boxes were full and no tarts were left over. What was the least number of boxes used by Howard?
To have the least number of boxes, Howard had to use as many as large boxes as possible.

If Howard used only large boxes,
number of large boxes used
= 392 ÷ 18
= 21 r 14 (x) There should be no remaining tarts left.

If 21 large boxes are used, there are 14 tarts left, Howard had to use less large boxes so that the rest of the tarts were packed in small boxes.

If Howard used 20 large boxes,
number of tarts to be packed in small boxes
= 392 - (20 x 18)
= 392 - 360
= 32

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

There should be no remaining tarts left. So, Howard had to use less large boxes.

If Howard used 19 large boxes,
number of tarts to be packed in small boxes
= 392 - (19 x 18)
= 392 - 342
= 50

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

Least number of boxes that Howard used
= 19 + 5
= 24

Answer(s): 24