Correct Answer: Option D

Explanation

let the number of N50 notes = x

let the number of N20 notes = y

from the first statement

x + y = 13.....(1)

from the second statement

50x + 20y = 530 ......(2)

dividing through by 10, we have

5x + 2y = 53 ....(20

solving simultaneously by eliminating

x + y = 12....(1)

5x + 2y = 53.....(2)

multiply eqn (1) by 2

multiply eqn (2) by 1

2x + 2y = 26

-5x + 2y = 53

-3x = -27

x = 9

substitute x = 9 into equation (1)

x + y = 13

y = 13 - x

= 13 - 9 = 4

y = 4

the number of N50 notes = 9

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