Gold is 19 times as heavy as water and copper is 9 times as heavy as water. In what ratio should these metals be mixed so that the mixture may be 15 times as heavy as water?

A travels 20 km with a speed of 40 km/hr. He travels another 45 km with a speed of 15 km/hr. what is his average speed for the entire journey?

The mean of four different observations is 17.5. When a new observation whose value 20 is added, what will be the new mean?   

The value of $$ \sqrt { 2^4} \ + \ ^{3}\sqrt {64} \  + \ ^4\sqrt { 2^8} \    $$ is :

Ram spends 40 % of his salary on food, 20% on house rent, 10% on entertainment and 10% on conveyance. If his savings at the end of a month are ₹ 1500, then his salary per month (in ₹) is:

A pipe of diameter d can drain a certain water tank in 40 minutes. The time taken by a pipe of diameter 2d for doing the same job in: 

The ratio of the number of coins of 25 paise, 50 paise, Rs.2 and Rs.5 is 5 ∶ 4 ∶ 3 ∶ 1, respectively. If the total amount of the coins is Rs.285, then the difference between the number of 25 paise and Rs.5 coins is: