A number X lies between 0 and 1. Which of the following is true?

If bc + cd = 2bd and a + c = 2b, then which one of the following is correct?

If (3a +6b +c +2d) x (3a - 6b - c +2d) = (3a - 6b +c- 2d) x (3a +6b - c- 2d), then which one of the following is correct ?

Which of the following interchanges of numbers would make the given equation correct? 8 x 20 / 3 + 9 - 5 = 38

If x + (1/y) = 1 and y + (1/z) = 1, then the value of z + (1/x) is

How many 7's are there in the following number series which are preceded by an even number but not followed by any odd number? 437523721367542742712276572