How many numbers can be formed from 1, 2, 3, 4, 5 (without repetition), when the digit at the units place must be greater than that in the ten's place?

+1 vote

How many numbers can be formed from 1, 2, 3, 4, 5 (without repetition), when the digit at the units place must be greater than that in the ten's place?

0 votes

1 cant be in units place

If 2 in units place 1 has to be in tens place

We can have 3×2×1 = 6 possible numbers here

If 3 is in units place than we can either 1 or 2 at tens place

Then we have 3×2×1×2 for the rest of the slots = 12 numbers

If 4 at units place we can have 1, 2 & 3 at tens

For 1, 2 & 3 we have 3×2×1×3 = 18 numbers

Similarly for 5 at units place we have 3×2×1×4 = 24 numbers

Total such numbers = 6 + 12 + 18 + 24 = **60 numbers.**

...