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Hello, teachers!

Please help me with this.

- All kinds of portable camping equipment is/are on sale for/at/on 30% in the store.

1. "Are" is the correct agreement, isn't it?

2. I think both "for" and "at" are correct, but the meanings are different, and "on" is incorrect. Am I right?

Thank you very much.
Peace!
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(1) 'Are' is grammatically correct, but proximity often overrules in practice, so that many would consider 'equipment is' more natural.

(2) Is the sale price only 30% of the regular price? If it is not, you need to indicate '30% off'. Yes, 'for/at 30% off' are right and 'on' is wrong.
Comments  
Students: We have free audio pronunciation exercises.
May I confirm this?

1. All kinds of portable camping equipment are on sale for/at 30% in the store.
- This means the price is $30 when the original price is $100.

2. All kinds of portable camping equipment are on sale [for/at - without] 30% off in the store.
- This means the price is $70 when the original price is $100.

Am I right?

All the best.
Your interpretations are correct, but the 'for' or 'at' is required in both cases.