The fourth proportional to 5, 8, 15 is:

Find the missing number:

2, 6, 12, 20, 30, 42, 56, (____)

 Which of the following fractions is less than 3/4 ? 

What is the difference in the place value of the digit 6 in the number 56761?

If the ratio of the areas of two circles is 9:25, find the ratio of their radii.

Which of the following sets of three numbers form a Pythagorean triplet?

 A basket has 5 apples and 4 oranges. Three fruits are picked at random. The probability that at least 2 apples are picked is 

Running at the same constant rate, 6 identical machines can produce a total of 270 bottles per minute. At this rate, how many bottles could 10 such machines produce in 4 minutes?

Two trains, each 250 m in length, are running on the same parallel tracks in opposite directions with speeds of 80 km/h and 70 km/h respectively. How long will it take for them to completely cross each other?