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If the overall average of first 20 multiples of two numbers is 924, what is the average of the two numbers?
- A76
- B44
- C88
- D80
Answer not set
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CCommunity
Let the numbers be ‘x’ and ‘y’
Sum of first 20 multiples of x = x(1 + 2 + … + 20) = (x × 20 × 21)/2 = 210x
Sum of first 20 multiples of y = y(1 + 2 + … + 20) = (y × 20 × 21)/2 = 210y
Their average = (210x + 210y)/40
⇒ 924 = 21(x + y)/4
⇒ x + y = 176
∴ Average of the two numbers = (x + y)/2 = 176/2 = 88
Sum of first 20 multiples of x = x(1 + 2 + … + 20) = (x × 20 × 21)/2 = 210x
Sum of first 20 multiples of y = y(1 + 2 + … + 20) = (y × 20 × 21)/2 = 210y
Their average = (210x + 210y)/40
⇒ 924 = 21(x + y)/4
⇒ x + y = 176
∴ Average of the two numbers = (x + y)/2 = 176/2 = 88