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The ratio of three numbers is 5 : 7 : 9 and their LCM is 2835. Find the sum of the greater number and the difference between the first two number
Question

The ratio of three numbers is 5 : 7 : 9 and their LCM is 2835. Find the sum of the greater number and the difference between the first two numbers.

A.

88

B.

85

C.

99

D.

80

Correct option is C

Given:

Ratio of three numbers = 5 : 7 : 9

Their LCM = 2835

Solution:

If numbers are in ratio a : b : c, then numbers = 5k, 7k, 9k.

LCM = LCM of (5,7,9) × k

Required sum = (greater number) + (difference of first two numbers).

= 5k,  7k,  9k

LCM of (5,7,9) = 315

So,

LCM of actual numbers = 315k

Equating given LCM

315k = 2835

k =2835315 \frac{2835}{315}​ = 9

Actual numbers

5k = 45, 7k = 63, 9k = 81

Greater number = 81

Difference between first two numbers = 63 - 45 = 18

Answer = 81 + 18 = 99

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