There are n n\,n marbles in a bag.
3 of the marbles are blue and the rest are white.
Thomas takes a marble from the bag at random and does not replace it. He then takes another marble at random from the bag.
The probability that Thomas takes two white marbles is 715\displaystyle \frac{7}{15}157
Show that 4n2−49n+90=04n^2 - 49n + 90 = 04n2−49n+90=0
Find the value of nnn.
