Let X and Y are given fractions.Given that, fraction X is thrice the fraction Y;i.e., X = 3Y ...(1)And their product = X x Y = 25/12Sub. eqn (1) in above,(3Y)x(Y) = 25/123(Y²) = 25/12(Y²) = 25/36Y = 5/6Hence the required fraction is 5/6.
Let the total length of pencil = L cm Then, black part = L/8∴ Remaining part = L - L/8 = 7L/ 8 and White part = (7L/8)/2 = 7L/8∴ Remaining part = L - (L/8 + 7L/16) = 7L/16∴ length of blue part = 7L/16According to the question, 7L/16 = 31/2⇒ 7L/16 = 7/2 ∴ L =8