Question

If no digit can be used more than once, find how many numbers that can be formed from the digits 3, 4, 5, 6, 7, 8 are greater than 7000.​

Answer 1

1 560

Explanation:

If no digit (from the digits 3, 4, 5, 6, 7, 8) can be used more than once :

we can form 6P5 = 720 (five-digit numbers) and they are all > 7000

we can form 6P6 = 720 (six-digit numbers) and they are all > 7000

if our number has four digits ,then the digit in the ten-thousands place of it must be 7 or 8 :

In this case :

we can form 5P3=60 number where the digit in the ten-thousands place of it is 7.

and we can form 5P3=60 number where the digit in the ten-thousands place of it is 8.

Final answer :

We can form 720+720+60+60 = 1 560 number greater than 7000