My Approach:
Total no of available digits: 5
No of 1-digit formed: 5
No of 2-digit formed: 4(excluding '0' on ten's place) * 4 (including zero – one among given digits already used)
No of 3-digit formed: 4(excluding '0' on 100th place) * 4 (including zero – one among given digits already used) * 3
No of 4-digit formed less than 4000: 3(excluding '0' & '4' on 1000th place) * 4 (including '0' & '4') * 3 * 2
No of 4-digit formed less than 4300 and greater than 4000: 3(excluding '3' & '4' on 100th place) * 3 (including '3') * 2
5 + (4*4) + (4*4*3) + (3*4*3*2) + (3*3*2)
So total of 175 natural numbers can be formed.
But answer is 158. Please explain how approach this kind of problems
Best Answer
Your calculations are correct, but $5 + (4*4) + (4*4*3) + (3*4*3*2) + (3*3*2)=159$,
not $175$, as blues66 suggested they probably didn't include $0$ as a solution