Number of coins

Algebra Level 1

While helping her mother to clean the house , Ron finds a box containing 20 pieces of 20sen and 50sen coins . The total value of all the coins is 760 sen . Find the number of 20sen coins .


The answer is 8.

Yitong Yab by Yitong Yab , 21, Singapore

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2 solutions

Abhishek Gorai
Aug 4, 2014

if all the coins were 50sen, then 20 coins makes 1000sen

the reduction (1000-760)=240 is due to presence of 20sen coins

each 20sen coin reduces 30sen, hence 240sen is reduced by 8 20sen coins

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Yitong Yab
Aug 2, 2014

let x = 20 sen y = 50 sen 20x + 50y = 760 2x + 5y = 76 ------- ( 1 ) x + y = 20 -------- ( 2 ) (2) *2 = 2x + 2y = 40 ----------- ( 3) (1) - (3) = 3y = 36 y = 12 50sen *12 = 600 sen 760sen - 600sen = 160sen 160sen = 20x x = 8

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