PSLE
The figure shows two stacks of identical styrofoam cups. There are 7 cups in the shorter stack and 12 cups in the longer one. The length of the shorter stack is 24 cm and the length of the longer stack is 34 cm. Justin wants to pack the styrofoam cups as a single stack into a box ⁷₁₀ m long. What is the most number of styrofoam cups he can pack into the box?
Difference in the height of styrofoam cups between the shorter and the longer stack
= 34 - 24
= 10 cm

Difference in the number of styrofoam cups between the shorter and the longer stack
= 12 - 7
= 5

Height of each increment
= 10 ÷ 5
= 2 cm

Number of increments in the shorter stack
= 7 - 1
= 6

Height of each styrofoam cup
= 24 - (6 x 2)
= 24 - 12
= 12 cm

1 m = 100 cm

⁷₁₀ m = ⁷₁₀ x 100 = 70 cm

Number of height increments that he can pack into the box
= (70 - 12) ÷ 2
= 58 ÷ 2
= 29 r 0

Number of styrofoam cups stacked on top of the first one = 29

Most number of styrofoam cups he can pack into the box including the first one
= 29 + 1
= 30

Answer(s): 30