Direction : What value should come in the place of question mark (?) in the following questions?

1798 ÷ 31 × ? = 348

If ' n ' be any natural number , then by which number ( n⁴-n ) is always divisible ? 

The population of Jaipur is 20,00,000. If it is increased by 5 %, 10%, 20% respectively in the next three years, then find the population of Jaipur after 3 years.

A number when divided by the sum of 555 and 445 gives two times their difference as quotient and 30 as the remainder. The number is: 

Present ages of Sameer and Anand are in the ratio of 5 : 4 respectively. Three years hence, the ratio of their ages will become 11 : 9 respectively. What is Anand's present age in years?

The average price of three furniture items is Rs 15,000. If the ratio of their prices is 3: 5: 7, then the cheapest furniture price is-

If (a-b)² + (b-c)² + (c-a)² = 0, then find the value of (a³+b³+c³-3abc) ?

Three pipes A , B and C takes 15, 24 and 36 minutes respectively to fill a tank. Pipe D can empty it in 1 hour. If all the four pipes are kept open then find the time taken to fill the tank.