"add up" vs "add right"

[Slawa]

English Language Tests, Intermediate level

ESL/EFL Test #165 "Phrasal Verbs (A to B)", question 2

When he tried to balance his checkbook, he found that things just didn't ..........

(a) add on
(b) add right
(c) add up

English Language Tests, Intermediate level

ESL/EFL Test #165 "Phrasal Verbs (A to B)", answer 2

When he tried to balance his checkbook, he found that things just didn't add up.

Correct answer: (c) add up

Your answer was: incorrect
When he tried to balance his checkbook, he found that things just didn't add right.
_________________________

Hi! Could you please explain "add up" and why it couldn't be "add right".
Thanks.

Slawa

[Mister Micawber]

.
'Add up' means 'produce an accurate total'.

'Add right' is not an idiomatic collocation in English ('add up right' would be OK).
.
_________________
Native English teacher at Mister Micawber's