PSLE
Luis packed 350 shortbreads into large and small boxes. He filled each large box with 16 shortbreads and each small box with 10 shortbreads. All the boxes were full and no shortbreads were left over. What was the least number of boxes used by Luis?
To have the least number of boxes, Luis had to use as many as large boxes as possible.

If Luis used only large boxes,
number of large boxes used
= 350 ÷ 16
= 21 r 14 (x) There should be no remaining shortbreads left.

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

If Luis used 20 large boxes,
number of shortbreads to be packed in small boxes
= 350 - (20 x 16)
= 350 - 320
= 30

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

Least number of boxes that Luis used
= 20 + 3
= 23

Answer(s): 23