In a triangle angles are in the ratio 3:4:5 , then the greatest angle is

In triangle angles are in the ratio $=3:4:5$

Let the angles are $3x,4x,5x$(say)

Total parts $=3x+4x+5x=12x$

Sum of angles in triangle $=180°$

One angle $=\frac{3x}{12x}\times 180°=45°$

$2^{\mathrm{nd}}$ angle $=\frac{4x}{12x}\times 180°=60°$

$3^{\mathrm{rd}}$ angle$=\frac{5x}{12x}\times 180°=75°$

$\therefore$Greatest angle $=75°$