less than 180 degrees = ?

[joham]

Random House-A Dictionary of Contemporary American Usage (1957), all:
All the angles in a triangle are less than 180 degrees.

I had thought we should say 'All the angles in a triangle are (= add up to) 180 degrees' and so was very surprised to read the 'less than' in this sentence. To me 'less than 180' means '<180'. But how can the three angles be '<180 degrees'?

Could I ask native speakers to help me please? Thank you in advance.

[Raymott]

Random House-A Dictionary of Contemporary American Usage (1957), all:
All the angles in a triangle are less than 180 degrees.

I had thought we should say 'All the angles in a triangle are (= add up to) 180 degrees' and so was very surprised to read the 'less than' in this sentence. To me 'less than 180' means '<180'. But how can the three angles be '<180 degrees'?

Could I ask native speakers to help me please? Thank you in advance.

"All angles in a triangle are less than 180 degrees" means "Angle A, angle B and angle C are each less than 180 degrees".
"All the angles are ..." does not mean "All the angles add up to ...".
If all the angles in a triangle are 60 degrees, you have an equilateral triangle, having (like all triangles) 180 degrees.

Compare:
All the girls in the family are less than 10 years old. They are 3, 5 and 7.
Their combined age is 15, but they are all under 10.