Robinson Tuition
Year 8 · Key Stage 3 · free KS3 maths worksheet

Congruent and similar shapes

12 original questions, 28 marks. Type your answers below for an instant mark and a score (algebra in any equivalent form, e.g. 2sqrt(3) or 2√3), or print the worksheet, mark it with the answers sheet, and use the solutions to see every step written out by hand.

Worksheet PDFWorked solutions PDFAnswers PDF

The questions

1

Here are the side lengths of four triangles.

Triangle A: 5 cm, 7 cm, 9 cm
Triangle B: 5 cm, 7 cm, 8 cm
Triangle C: 9 cm, 7 cm, 5 cm
Triangle D: 5 cm, 6 cm, 9 cm

Write down the letters of the two triangles that are congruent to each other.

1 mark
Show answer
A and C
2

Lena says, "If two triangles have the same three angles, they must be congruent."

  1. Write down the four conditions that do show two triangles are congruent.
  2. Explain why Lena is wrong.
2 marks
Show answer
a) SSS, SAS, ASA, RHS b) open: Equal angles only show the triangles are similar. One could be an enlargement of the other, so they need not be the same size.
3

In triangles PQR and XYZ,

PQ = XY = 6 cm
angle PQR = angle XYZ = 40°
QR = YZ = 8 cm

The two triangles are congruent.

Write down the congruence condition that shows the triangles are congruent.

1 mark
Show answer
SAS
4

The diagram shows triangle PQR and triangle XYZ.

Are the two triangles congruent? Give a reason for your answer.

PQR6 cmXYZ6 cm50°70°50°70°Diagram NOT accurately drawn
2 marks
Show answer
Yes - two angles and the side between them are equal (ASA)
5

Triangle ABC is congruent to triangle DEF.

A corresponds to D, B corresponds to E and C corresponds to F.

AB = 7 cm, BC = 9 cm, angle ABC = 48° and angle BCA = 71°.

  1. Write down the length of EF.
  2. Write down the size of angle DEF.
  3. Work out the size of angle EDF.
3 marks
Show answer
a) 9 cm b) 48° c) 61°
6

Rectangle A measures 4 cm by 6 cm.

Rectangle B is mathematically similar to rectangle A. The shorter side of rectangle B is 10 cm.

  1. Work out the scale factor of the enlargement from A to B.
  2. Work out the length of the longer side of rectangle B.
2 marks
Show answer
a) 2.5 b) 15 cm
7

Triangle ABC is similar to triangle PQR.

AB corresponds to PQ, and BC corresponds to QR.

AB = 6 cm, PQ = 9 cm and BC = 8 cm.

Work out the length of QR.

2 marks
Show answer
12 cm
8

Triangles ABC and PQR are mathematically similar.

Angle ABC = angle PQR and angle BCA = angle QRP.

  1. Work out the length of QR.
  2. Work out the length of AC.
ABC4 cm6 cmPQR6 cm7.5 cmDiagram NOT accurately drawn
3 marks
Show answer
a) 9 cm b) 5 cm
9

Jamal is 1.6 m tall. At 4 pm his shadow is 2 m long.

At the same time, a flagpole next to him casts a shadow 9 m long.

The sun makes similar triangles with Jamal and with the flagpole, as shown in the diagram.

Work out the height of the flagpole.

2 m1.6 m9 mhJamalflagpoleDiagram NOT accurately drawn
3 marks
Show answer
7.2 m
10

ABCD is a kite in which AB = AD and CB = CD.

The diagonal AC is drawn.

Prove that triangle ABC is congruent to triangle ADC.

ABCDDiagram NOT accurately drawn
3 marks
Show answer
Triangle ABC is congruent to triangle ADC by SSS
11

The straight lines AD and BC cross at M.

AM = MD and BM = MC.

Prove that triangle ABM is congruent to triangle DCM.

ABCDMDiagram NOT accurately drawn
3 marks
Show answer
AM = DM (given), BM = CM (given), angle AMB = angle DMC (vertically opposite), so the triangles are congruent by SAS
12

In triangle ABC, D is a point on AB and E is a point on AC.

DE is parallel to BC.

AD = 4 cm, DB = 6 cm and DE = 5 cm.

Work out the length of BC.

4 cm6 cm5 cmABCDEDiagram NOT accurately drawn
3 marks
Show answer
12.5 cm

Your score

Answer the questions above and your score appears here.

Every question here is original and written by Robinson Tuition. It follows the Key Stage 3 programme of study; Year 9 sheets end with extension questions for top sets.

All Year 8 topics