(a) $280

in shop A, it is $280 less $6x 270/30, or less $54

in shop B, it is less 20% x $280, or less $56.

buy from shop B to save more#

(b) net amount after discount is $168. Every $30 deduct $6. 

Assume if above $150, deduct $6×5,

168 + $6×5 =$198 (already above $180, then would have entitled deduction of $6×6)

168 + $6×6 = $204# (ok, answer is still below $210)

(c)  $38.40 / 80% = $48 original price

in shop A, can only deduct $6. 

Percentage discount is 6/48 = 12.5%#

Hi SahMom,

Can you please explain your comment “(ok, answer is still below $210)”?

If the amount before discount is $210,

210 / 30 = 7

7 × 6 = 42

210 – 42 = $168

So shouldn’t $210 be an acceptable answer too?

Hi BigDevil, oh yes!  you are right $210 is acceptable too. I worked from bottom and forgot to check upwards for $210.

Mr Lim could be a very smart man to work his purchase budget right up to $210 and square off the net amount paid. i.e. Additional $6 purchase cost but also additional $6 deduction   entitlement. 🙂