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ICSE Class 10 Answered

A box contains some black balls and 30 white balls. If the probability of drawing a black ball is two-fifths of a white ball, find the number of black balls in the box.
Asked by defence | 07 Mar, 2019, 08:53: PM
answered-by-expert Expert Answer
Let number of black balls be n in the box
 
probability of selecting the black ball at random = begin mathsize 12px style fraction numerator n over denominator n plus 30 end fraction end style
probability of selecting the white ball at random = begin mathsize 12px style fraction numerator 30 over denominator n plus 30 end fraction end style
given : begin mathsize 12px style fraction numerator n over denominator n plus 30 end fraction space equals space 2 over 5 space fraction numerator 30 over denominator 30 space plus space n end fraction space space space space space space o r space space space n space equals space 2 over 5 cross times 30 space space equals space 12 end style
number of black balls = 12
Answered by Thiyagarajan K | 07 Mar, 2019, 11:37: PM

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