If and are chosen uniformly and randomly, with replacement, from the set . Determine the probability that the roots of the equation are real.
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F i r s t o f a l l , t h e t o t a l n u m b e r o f o u t c o m e s c a n b e e a c h n u m b e r w i t h a l l o t h e r s , i . e . ( 1 , 1 ) ; ( 1 , 2 ) . . . . . ( 1 0 , 9 ) ; ( 1 0 , 1 0 ) w h i c h i s a 1 0 0 o u t c o m e s . N o w f o r x 2 + p . x + q = 0 t o h a v e r e a l r o o t s , w e n e e d p 2 ≥ 4 q S o , b y r e j e c t i n g c a s e s a n d b y r e c o g n i z i n g a p a t t e r n , W e c a n s e e f o r p = 1 , q h a s n o v a l u e . p = 2 , q = 1 p = 3 , q = 1 , 2 p = 4 , q = 1 , 2 , 3 , 4 p = 5 , q = 1 , 2 , 3 , 4 , 5 , 6 p = 6 , q = 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 p = 7 , 8 , 9 , 1 0 ; q = a l l t h e n u m b e r s . S o t o t a l n u m b e r o f p a i r s p o s s i b l e = 1 + 2 + 4 + 6 + 9 + 1 0 + 1 0 + 1 0 + 1 0 = 6 2 S o , p r o b a b i l i t y = 1 0 0 6 2 = 0 . 6 2