Answer:
23 yellow, 30 pink and 12 blue balls
Explanation:
Let the number of yellow, pink, blue, and black balls be y, p, b, and x respectively.
From 1st sentence:
y +p +b +x= 90
"60 of them are not pink"
➜ y +b +x= 60
Given that 25 are black, x= 25.
"67 of them are not yellow"
➜ p +b +x= 67
Subst. x= 25 into the above equations:
y +p +b +25= 90
y+ p +b= 65 -----(1)
y +b +25= 60
y +b= 35 -----(2)
p +b +25= 67
p +b= 42 -----(3)
I will rewrite the 3 equations for better clarity:
y +p +b= 65 -----(1)
y +b= 35 -----(2)
p +b= 42 -----(3)
(1) -(2):
p= 65 -35
p= 30
(1) -(3):
y= 65 -42
y= 23
Substitute p= 30 and y= 23 into (1):
23 +30 +b= 65
b= 65 -53
b= 12
Thus, there 23, 30 and 12 yellow, pink and blue balls respectively.