The inner angles of a triangle are proportional to the numbers 3, 5 and 7. What is the largest of its angles?

The easiest way to solve this problem is to write an equation based on its condition.
But first, remember that the sum of all the angles in a triangle is 180 °.
Let x be one part, then the first side of the triangle is 3x, the second side of the triangle is 5x, and the third is 7x. Since their sum is 180 °, we have the following equation:
3x + 5x + 7x = 180;
15x = 180;
x = 180: 15;
x = 12 – one part;
Now we can find the largest angle in this triangle:
7 * 12 = 84 ° – this is option number 4;
Answer: 84 °.