At Mdm Salma's fruit stall, some oranges had been sold by noon. The ratio of the number of oranges sold to the number still unsold was 3 : 2. No oranges were added during the day. In the afternoon, 100 more oranges were sold. After this, 15% of the original stock was still unsold.
- How many oranges were there in the original stock?
- How many oranges were still unsold at noon?
Need a hint?
Compare the fraction left at noon with the fraction left at the end. The 100 oranges are the difference between these two fractions of the original stock.
Worked answer
- At noon, the unsold fraction was 2 ÷ (3 + 2) = 25.
- After the afternoon sale, the unsold fraction was 15% = 320.
- The fraction sold in the afternoon was 25 − 320 = 14.
- The original stock was 100 ÷ 14 = 400 oranges.
- The number unsold at noon was 25 × 400 = 160 oranges.
The mistake this question tests
Calculation slip
A common mistake is to treat the 100 oranges sold in the afternoon as 320 of the original stock. They represent the difference between the noon remainder 25 and the final remainder 320.
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