A 4-digit number is formed by using four of the seven digits 1, 3, 4, 5, 7, 8 and 9. No digit can be used more than once in any one number. Find how many different 4-digit numbers can be formed if
- (i)there are no restrictions,[2]
- (ii)the number is less than 4000,[2]
- (iii)the number is even and less than 4000.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2010). The mark or mark type is shown in brackets.
- [B1] (i) 7 × 6 × 5 × 4
- [B1] (i) 840
- [M1] (ii) 2 × 6 × 5 × 4 or ²⁄₇ × (840)
- [A1] (ii) 240
- [M1] (iii) 2 × 5 × 4 × 2 or ²⁄₆ × (240) or clear indication of method
- [A1] (iii) 80
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