I got involved in a discussion about some Math problems provided in the local primary school education:
- 20 more than 543 is 563
- 25 less than 261 is 236
- 155 less than 310 is 155
- 355 more than 1233 is 1588
Some of us (including me) argued that this is unclear or incorrect English, while others said that it is correct or that we are not creative if we do not understand it (huh?).
In my own Math education, I have learnt that "less than" and "more than" (or rather, "greater than") are comparative operators. However, in the above, they are used as manipulative operators (subtraction or addition) - a usage I never learnt.
At first I thought this must be something peculiar with the Singapore Math education, as those who argued that this is incorrect are mostly foreigners, while the other side is made up of mostly locals.
After some searching for similar use on the Internet, the two instances I could find are an exercise paper from Math Activities Resource Center, Mt. San Antonio College, Walnut, CA (USA) [link], and a lecture paper from Professor Weissman's Algebra Classroom [link].
In the exercise paper, the lecturer also mentions that "less than" is different from "is less than", in that "less than" is used to mean subtraction (where the numbers are inverted), whereas "is less than" is used to compare two numbers.
In the lecture paper, it is mentioned that "3 is less than 7" translates to "3<7", "3 less than 7" translates to "7-3" and "3 less 7" translates to "3-7".
I want to hear from some experts regarding how correct and/or widespread this kind of usage of these terms is. No matter how many times I read the examples back to myself I feel it's odd and wrong to use it this way, and that the correct usage for manipulation should be:
- 20 added to 543 is 563
- 25 subtracted from 261 is 236
- 155 subtracted from 310 is 155
- 355 added to 1233 is 1588
Whereas the correct usage for comparison should be:
- 20 more than 543 is False
- 25 less than 261 is True
- 155 less than 310 is True
- 355 more than 1233 is False