# Mr Tan has an equal number of pens and pencils. He puts the pens in bundles of 8 and the pencils in bundles of 12. There are 15 bundles altogether. How many pens are there?

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let the number of bundles formed by pencil be y.

acc. to 1st condition;

8x=12y

therefore 12y-8x=0----(i)

acc.to the 2nd condition;

y+x=15----(ii)

multiplying (ii) by 8;

8y+8x=120---(iii);

adding (i) and (iii);

12y-8x=0

8y+8x=120

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20y=120

y=6;

therefore x=15-y=15-6=9(from eqn (ii));

total no. of pens=8x=8*9=72 pens.