We know that ,
Average = `("Sum of the quantities")/("Number of the quantities")`
`therefore ("Wages of 50 workers")/(50) = 100`
`implies "Wage"_(50) = 50 xx 1000 ` = ₹ 5000
Similarly ,
`("Wage"_(30))/(30) = 120 implies "Wage"_(30) = 30 xx 120 = ` ₹ 3600
Now ,
Wage of 20 workers = `"Wage"_(50) - "Wage"_(30)`
= 5000 - 3000
= ₹ 1,400
`implies` Average `"wage"_(20) = (1400)/(20)` = ₹ 70
`therefore` Hence , option (b) is the correct answer .