Hui Min had a roll of ribbon. She used 35% of the ribbon to wrap a gift box. She then used 40% of the remaining ribbon to make a card. The rest of the ribbon was not used. (a) What percentage of the whole roll of ribbon was not used? (b) The length of ribbon that was not used was 78 cm. How long was the ribbon that she used to wrap the gift box?

PercentageStructured · 3 marks

Hui Min had a roll of ribbon. She used 35% of the ribbon to wrap a gift box. She then used 40% of the remaining ribbon to make a card. The rest of the ribbon was not used.

What percentage of the whole roll of ribbon was not used?
The length of ribbon that was not used was 78 cm. How long was the ribbon that she used to wrap the gift box?

Need a hint?

For (a), the 40% is taken from what was left after the gift box, not from the whole roll. For (b), find 1% first.

(a) After the gift box, the ribbon left is 100% − 35% = 65% of the roll.
She used 40% of this remainder for the card, so 60% of the remainder is not used.
60% of 65% = (60 ÷ 100) × 65 = 39% of the whole roll was not used.
(b) 39% of the roll is 78 cm.
1% of the roll = 78 ÷ 39 = 2 cm.
The gift box used 35%, which is 35 × 2 = 70 cm.

Answer: 70 cm

Habit

Many pupils take 100% − 35% − 40% = 25% in (a), but the 40% is only of the remaining ribbon, not of the whole roll.