PSLE
Sean packed 318 croissants into large and small boxes. He filled each large box with 18 croissants and each small box with 10 croissants. All the boxes were full and no croissants were left over. What was the least number of boxes used by Sean?
To have the least number of boxes, Sean had to use as many as large boxes as possible.

If Sean used only large boxes,
number of large boxes used
= 318 ÷ 18
= 17 r 12 (x) There should be no remaining croissants left.

If 17 large boxes are used, there are 12 croissants left, Sean had to use less large boxes so that the rest of the croissants were packed in small boxes.

If Sean used 16 large boxes,
number of croissants to be packed in small boxes
= 318 - (16 x 18)
= 318 - 288
= 30

Number of small boxes needed to pack 30 croissants
= 30 ÷ 10
= 3 (✓) There is no remaining croissants left.

Least number of boxes that Sean used
= 16 + 3
= 19

Answer(s): 19