Diagonal AC is drawn in rhombus ABCD. Find the angle ABC if the angle ACD is known to be 10 degrees.

To solve this problem, we need to know that the ACD and BAC angles are equal, due to the fact that, by the definition of a rhombus, the angles that lie crosswise are always equal. As a result, we get that the triangle formed as a result of our diagonal AC is isosceles. Thanks to this, we can find out that if this is an isosceles triangle, then the angles at the base are equal: BAC = BCA = 10 °, and the angle B = 180 ° – 10 ° – 10 ° = 160 °.
Answer: angle B = 160 °.