Explanation : (D) Given that, sides of a cuboid are 5cm, 2cm and 5cm.
Volume of cuboid = 5 × 2 × 5 = 50cm3
Let the side of the cube formed with minimum number of cuboids = x
Hence, volume of the cube = x3
Let, number of cuboids required = n
Hence, n × 50 = x3
n × 50 must be perfect cube i.e.
minimum value of n = 2 × 2 × 5 = 20
Volume of the cube formed = 20 × 50 = 1000 cm3
So, required cuboids = 20
Explanation : (A) In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is the sum of its positive divisors excluding the number itself, so from the option, only 28 is the perfect number. i.e. 28 = 1 + 2 + 4 + 7 + 14
Explanation : (D) If the ratio is 1 : 4, Then the number of defective bulbs = x and number of good bulbs = 4x
∴ x + 4x = 12
⇒ 5x = 12
which is not possible for any integral value of x.
So, 1 : 4 is not possible.
Explanation : (A) Diagnostic evaluation refers to the evaluation procedure aims to diagnose the nature and degree of learning difficulties faced by the learner. It involves gathering information about learners' errors, nature of errors, possible reasons of errors, level of conceptual understanding and possible interventions to rectify the errors.