$${a\over b}={2\over3}$$ and $${b\over c}={4\over5}$$ then the ratio  $${a+b}\over {b+c}$$ equal to:

A boat travel 240 km downstream in 3 hours and the time is taken by the boat to travel the same distance in upstream in 6 hours. Find the speed of stream (in kmph).

A number, on subtracting 15 from it reduces to its 80 %. What is 40 % of the number? 

There are 80 students in a class out of these 15% are girls. The monthly fee of each girl is Rs.350 and monthly fee of each boy is 38% more than each girl. What is the total fee of girls and boys in the class?

An article listed at 800 is sold at successive discounts of 25 % and 15 %. The buyer desires to sell it off at a profit of 20 % after allowing a 10 % discount. What would be his list price?

Direction: Study the pie chart carefully and answer the given questions. The pie chart shows the percentage breakup of students in different classes from VI to X in the year 2017

If in class VI, the ratio of boys to girls is 6:5 and the total number of girls in class VI is 50 less than that of the total number of girls in class VII. Find the ratio of the total number of boys in class VI to class VII.

Two guns were fired from the same place at an interval of 13 minutes but a person in a train approaching the place hears the second shot 12 minutes 30 seconds after the first. Find the speed of train if sound travels at 330 metres per second.

If a-b=10 and ab=-21, then what is the value of a³-b³?