Make the greatest and the smallest 4-digit numbers using the digits 5, 4, 7 and 9 (without repeating the digits) and with the condition that:

(i) 7 is at unit’s place

The smallest 4-digit number using the digits 5, 4, 7 and 9, and keeping 7 at unit’s place = 4597

The greatest 4-digit number using the digits 5, 4, 7 and 9 and keeping 7 at unit’s place = 9547

(ii) 9 is at ten’s place

The smallest 4-digit number using the digits 5, 4, 7 and 9 and keeping 9 at ten’s place = 4597

The greatest 4-digit number using the digits 5, 4, 7 and 9 and keeping 9 at ten’s place = 7594

(iii) 4 is at hundred’s place

The smallest 4-digit number using the digits 5, 4, 7 and 9 and keeping 4 at hundred’s place = 5479

The greatest 4-digit number using the digits 5, 4, 7 and 9 and keeping 4 at hundred’s place = 9475