RGS Primary 2009 PSLE Math Prelim Paper 2 Q13

The figure below is made up of a big circle, square and a small circle. The area of the square is 400 square cm. Find the area of the shaded region. (Correct your answer to 2 decimal places)

Solution

Area of square --> 400 square cm
Length of square --> 20 cm (square root of 400 sq cm)

Area of 1/4 square

--> 400 square cm divided by 4

= 100 square cm

Area of one right-angle triangle -->(1/2)(b)(h)

100 square cm = (1/2)(r)(r)

(r)(r) = (100 square cm) x 2 = 200 square cm

Area of circle = (3.14)(r)(r)

=(3.14)(200 square cm)

= 628 square cm

Shaded area -->(628 - 400) square cm

= 228 square cm
= 228.00 square cm (correct to 2 decimal places)

Answer: 228.00 square cm

Printer Friendly Version

CHIJ St Nicholas Girls' Sch 2009 P6 SA1 Paper 2 Q12

The figure below is made up of 2 squares and a rectangle. The ratio of the area of A to the area of B to the area of C is 9:4:3. The ratio of the unshaded part of B to the unshaded part of C is 4:1. If the shaded part is 56 square cm, find the area of A that is not covered by B.

Solution

(C) 3 parts --> 56 sq cm + 1 unit
(multiply by 4)
(C) 12 parts --> 224 sq cm + 4 units
(B) 4 parts --> 56 sq cm + 4 units

12 parts - 4 parts --> 224 sq cm - 56 sq cm
8 parts --> 168 sq cm
1 part --> 168 sq cm divided by 8 = 21 sq cm

(A - B) 5 parts --> 5 x 21 sq cm = 105 sq cm

Answer: 105 square cm

Printer Friendly Version

Rosyth Sch 2007 PSLE Math Prelim Q45

The figure shows a cube with 3 painted parts A, B and C. These painted parts are of the same area and they are touching the midpoints of the sides of the cube. The total area of the painted parts is 54 square cm. Find the volume of the cube.

3 painted parts on 3 faces of the cube ----- 54 square cm

1 painted part on 1 face of the cube
54 square cm divided by 3 = 18 square cm

Area of 1 triangle is 18 square cm divided by 2
= 9 square cm

For area of triangle to be 9 square cm, the base has to be 6 cm and height has to be 3 cm as worked out below
(1/2 x 6 cm x 3 cm = 9 square cm)

1 side of the cube is therefore 6 cm as seen from above diagram.

Volume of cube
(6 x 6 x 6) cubic cm = 216 cubic cm

Answer: 216 cubic cm