Kai has a rectangular metal lunch box. Its length, breadth and height are whole numbers of centimetres. The top face (length × breadth) has an area of 88 cm², while the front face (length × height) has an area of 77 cm². The length is longer than the breadth, and the breadth is longer than the height. What is the area of the right face of the lunch box?
- 56 cm²
- 77 cm²
- 88 cm²
- 165 cm²
Need a hint?
Find the side length shared by the top and front faces. The clue about which side is longest helps you choose the correct common factor.
Worked answer
- The top and front faces both contain the length, so the length is a common factor of 88 and 77.
- Their common factors are 1 and 11. Only 11 cm can be longer than the other two sides.
- The breadth is 88 ÷ 11 = 8 cm and the height is 77 ÷ 11 = 7 cm.
- The right face has an area of 8 × 7 = 56 cm².
The mistake this question tests
Factors and multiples (HCF, LCM)
A common mistake is to copy one of the given face areas because both are areas of faces. The right face uses the breadth and height, so these must be found first.
How to fix it at home →More PSLE area & volume questions
Nadia glued some 1-cm wooden cubes together to form a cuboid
See the answer →Short answer · 2mMr Faizal had 27 identical small cubes for a school exhibition
See the answer →Short answer · 2mNoah's craft box has a square base with an area of 49 cm²
See the answer →Structured · 5mThree identical rectangles are placed side by side to form one large rectangle
See the answer →Structured · 3mA decorative border is made of 4 identical semicircular tiles
See the answer →Structured · 5mTwo rectangular containers P and Q hold water
See the answer →Practise PSLE area & volume until the mistakes stop.
Three PSLE questions, free, no sign-up. You’ll see exactly where the marks went. Then 7 days of everything for S$4.99.