Questions

The central nervous system ( brain and spinal card ) are invested with the meninges which nourish and protect the system .This again is enclosed inside a bony box which has the skin above it

A tetrad is formed from two homologous chromosomes, each consisting of two chromatids in the first stage of meiosis called prophase1.

The International Day for Biological Diversity (IDB) is observed every year on May 22 to increase understanding and awareness of biodiversity issues. The 2017 theme “Biodiversity and Sustainable Tourism” provides an opportunity to raise awareness and action towards the important contribution of sustainable tourism both to economic growth and to the conservation and sustainable use of biodiversity.

Let the two digits be x & y

From given data in the question, we get

x + y = 3(x - y)

x + y = 3x - 3y

=> 2x = 4y

x/y = 2/1

For having the 2:1, numbers satisfying are

12, 21, 24, 42, 36, 63, 48, 84

From this 36 is eleminated because it is a perfect square and no others are prime or perfect squares.

Hence, there exists 7 such 2-digit numbers => 12, 21, 24, 42, 63, 48, 84.