L7 · Angle relationships in triangles

1. 1.

   Two angles of a triangle measure 57° and 76°. Find the third angle.

   Answer. 47°

   57 + 76 + x = 180 → x = 47.

2. 2.

   Two angles of a triangle measure 55° and 43°. Find the third angle.

   Answer. 82°

   55 + 43 + x = 180 → x = 82.

3. 3.

   Two angles of a triangle measure 35° and 61°. Find the third angle.

   Answer. 84°

   35 + 61 + x = 180 → x = 84.

4. 4.

   Two angles of a triangle measure 70° and 39°. Find the third angle.

   Answer. 71°

   70 + 39 + x = 180 → x = 71.

5. 5.

   Two angles of a triangle measure 66° and 61°. Find the third angle. Then Nora needs 3 of that amount. What is the total they need?

   Answer. 159°

   66 + 61 + x = 180 → x = 53. Then multiply by 3: 159°.

6. 6.

   Two angles of a triangle measure 45° and 64°. Find the third angle. Then Luis needs 4 of that amount. What is the total they need?

   Answer. 284°

   45 + 64 + x = 180 → x = 71. Then multiply by 4: 284°.

7. 7.

   Two angles of a triangle measure 34° and 30°. Find the third angle. Then Nora needs 3 of that amount. What is the total they need?

   Answer. 348°

   34 + 30 + x = 180 → x = 116. Then multiply by 3: 348°.

8. 8.

   Two angles of a triangle measure 41° and 67°. Find the third angle. Then Grace needs 2 of that amount. What is the total they need?

   Answer. 144°

   41 + 67 + x = 180 → x = 72. Then multiply by 2: 144°.

9. 9.

   Two angles of a triangle measure 51° and 41°. Find the third angle. Then Mei needs 5 of that amount. What is the total they need?

   Answer. 440°

   51 + 41 + x = 180 → x = 88. Then multiply by 5: 440°.

10. 10.

    Two angles of a triangle measure 40° and 51°. Find the third angle. Then Sam needs 4 of that amount. What is the total they need?

    Answer. 356°

    40 + 51 + x = 180 → x = 89. Then multiply by 4: 356°.

11. 11.

    Think

    Grace tried this problem:
    Two angles of a triangle measure 54° and 50°. Find the third angle.
    Grace wrote 152°. That is not correct. What is the right answer?

    Answer. 76°

    Grace’s answer 152° is off. 54 + 50 + x = 180 → x = 76.

12. 12.

    Think

    Grace tried this problem:
    Two angles of a triangle measure 54° and 44°. Find the third angle.
    Grace wrote -82°. That is not correct. What is the right answer?

    Answer. 82°

    Grace’s answer -82° is off. 54 + 44 + x = 180 → x = 82.

Original extra practice. Keys are computed from the items, not guessed.