1 . There are two taps Aand Bto fill up a water tank. The tank can be filled in 40 min, if both taps are on. The same tank can be filled in 60 min, if tap Aalone is on. How much time will tap Balone take, to fill up the same tank?
2 . A train started from a station with a certain number of passengers. At the first halt, $1\over 3$rd of its passengers got down and 120 passengers got in. At the second halt, half of the passengers got down and 100 persons got in. Then, the train left for its destination with 240 passengers. How many passengers were there in the train when it started ?
4 . A person has four iron bars whose lengths are 24 m, 36 m, 48 m and 72 m respectively. This person wants to cut pieces of same length from each of four bars. What is the least number of total pieces if he is to cut without any wastage?
7 . Read the following information carefully to answer the questions that follow
The average age of 6 persons living in a house is 23.5 years. Three of them are majors and their average age is 42 years. The difference in ages of the three minor children is same What is the mean of the ages of minor children?