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If the ratio is 2 : 3 then in a class of 5 there would be 2 boys and 3 girls. 

So we can say that 2/5 of the class are boys and 3/5 of the class are girls. 

And we know that to calculate 3/5...

y = 2x + 5 y = 4, therefore 2x + 5 = 4 2x = 1 x = 1/2

a² + b² = c²

a : 9       b : unknown      c: 15

b² =c² - a²

so b² = 225 - 81

=144 so b=12

42 x 5 = 210.

45+29+63+42 = 179.

210 - 179 = 31

X = 31

3x^2+18x-1 Bracket out 3x^2+18x  Factorise by bringing out the common factor of 3 = 3(x^2+6x) Divide the x coefficient by 2  =  3(x^2+3x) And then remove the square on the x^2 variable and add a square to...