How does one use guess and check? Guess 143 out of nowhere oh it works ok then that is my answer

① Guess for 1 person
② Calculate the other person based on the first person
③ Addd the two and see if it tallied with the sum.

They use a list for this

Eg.

Guess :

Sean : 100
Matthew : 168 + 100 = 268
Total 268 + 100 = 368 (✗)

Sean : 140
Matthew : 168 + 140 = 308
Total 308 + 140 = 448 (✗)

Sean : 143
Matthew : 168 + 143 = 311
Total 311 + 143 = 454 (✓)

Then the question is largely determined by whether one can see the pattern in the list lol ok interesting

The idea is to keep increasing or decreasing until the right total is achieved.

P4 they are taught guess and check, but it's merely one of the heuristic methods. At P5 and 6 they would do models or units method like what good Samathritan has presented. Much faster

Also, if you get the first guess correct, full marks will be given (for those questions where the alternative method is supposition/assumption)

I see