PSLE
Bobby packed 402 croissants into large and small boxes. He filled each large box with 10 croissants and each small box with 6 croissants. All the boxes were full and no croissants were left over. What was the least number of boxes used by Bobby?
To have the least number of boxes, Bobby had to use as many as large boxes as possible.

If Bobby used only large boxes,
number of large boxes used
= 402 ÷ 10
= 40 r 2 (x) There should be no remaining croissants left.

If 40 large boxes are used, there are 2 croissants left, Bobby had to use less large boxes so that the rest of the croissants were packed in small boxes.

If Bobby used 39 large boxes,
number of croissants to be packed in small boxes
= 402 - (39 x 10)
= 402 - 390
= 12

Number of small boxes needed to pack 12 croissants
= 12 ÷ 6
= 2 (✓) There is no remaining croissants left.

Least number of boxes that Bobby used
= 39 + 2
= 41

Answer(s): 41