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Maths homework

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My ten year old has this problem to solve

I have X roses. 80% are white, the rest are red. I add 76 white and 48 red. Now 75% are white. What is the value of X?

I have worked out the answer using a spreadsheet but he needs to show workings.

Any ideas?

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Bit late in seeing this, but:

X = W+R, where W is the no of White Roses and R is the no of Red.

The ratio of 80% W means W=4R, or 0.25W=R.

When you add the other roses:

Total new no of White/total new no of roses = 0.75

(76+W)/((76+W)+(48+R))=0.75 ;

substitute in either of the above values for R or W:

(76+W)/((76+W)+(48+0.25W))=0.75;

(76+W)=57+0.75W+36+0.1875W;

0.0625W=17

W=272

therefore R=272/4=68

X=272+68=340

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7 hours ago, nickthejag said:

Bit late in seeing this, but:

X = W+R, where W is the no of White Roses and R is the no of Red.

The ratio of 80% W means W=4R, or 0.25W=R.

When you add the other roses:

Total new no of White/total new no of roses = 0.75

(76+W)/((76+W)+(48+R))=0.75 ;

substitute in either of the above values for R or W:

(76+W)/((76+W)+(48+0.25W))=0.75;

(76+W)=57+0.75W+36+0.1875W;

0.0625W=17

W=272

therefore R=272/4=68

X=272+68=340

Correct :thumbsup2:

Thanks Nick.

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