Can three lengths make a triangle?

Answer Key - Grade 8 Math Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   Ari has three paper strips: 6.4 cm, 3.8 cm and 9.1 cm. Can they make a triangle?

   • No: 9.1 cm is longer than 3.8 cm
   • Yes: 3.8 + 6.4 = 10.2 cm, longer than 9.1 cm
   • No: a triangle needs three equal sides, so these cannot work
2. 2.

   Bo has three pieces of yarn: 12 cm, 7.5 cm and 5.5 cm. Can they make a triangle?

   • No: a triangle needs three equal sides to join up
   • No: 12 cm is longer than 5.5 cm
   • Yes: 5.5 + 7.5 = 13 cm, longer than 12 cm
3. 3.

   Luz has two paper strips, 3.5 cm and 8 cm, for two sides of a triangle. The third side is more than ? cm and less than ? cm. Type both numbers, smaller first.

   4.5, 11.5
4. 4.

   Milo has two pieces of yarn, 2.7 cm and 6.2 cm, for two sides of a triangle. The third side is more than ? cm and less than ? cm. Type both numbers, smaller first.

   3.5, 8.9
5. 5.

   Pia has two paper strips, 2.5 cm and 10 cm, for two sides of a triangle. The third side is more than ? cm and less than ? cm. Type both numbers, smaller first.

   7.5, 12.5
6. 6.

   Tala has 3.6 cm and 8.4 cm pieces of yarn for two sides of a triangle. Which length can the third side be?

   • 10.5 cm
   • 12.5 cm
   • 4.8 cm
   • 3.9 cm
7. 7.

   Zee has 2.8 cm and 6.5 cm paper strips for two sides of a triangle. Which length can the third side be?

   • 9.8 cm
   • 9.3 cm
   • 4 cm
   • 3.5 cm
8. 8.

   Ari has paper strips of 3.4 cm and 6.9 cm for two sides of a triangle. The third side is a whole number of cm. What is the longest it can be?

   10
9. 9.

   Bo has pieces of yarn of 5.6 cm and 8.7 cm for two sides of a triangle. The third side is a whole number of cm. What is the longest it can be?

   14
10. 10.

    Esme has paper strips of 2.2 cm and 9.5 cm for two sides of a triangle. The third side is a whole number of cm. What is the longest it can be?

    11