Wong YX's answer to Jasmine 's Primary 5 Maths Whole Numbers Singapore question.
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When the 2 new books are added, the average cost of books increased from $8.50 to $10, or increased by:
$10 - $8.50 = $1.50
At the same time, the average cost of the 2 new books decreased from $13 to $10, or decreased by:
$13 - $10 = $3 each
In total, the total decrease in cost of the 2 new books is:
$3 x 2 = $6
Where did the $6 go to? The $6 went to make up the increase in the average cost of books mentioned in the 1st step. Hence, the total number of books at first was:
$6 ÷ $1.50 = 4
By adding 2 new books, the total number of books in the end is:
4 + 2 = 6
$10 - $8.50 = $1.50
At the same time, the average cost of the 2 new books decreased from $13 to $10, or decreased by:
$13 - $10 = $3 each
In total, the total decrease in cost of the 2 new books is:
$3 x 2 = $6
Where did the $6 go to? The $6 went to make up the increase in the average cost of books mentioned in the 1st step. Hence, the total number of books at first was:
$6 ÷ $1.50 = 4
By adding 2 new books, the total number of books in the end is:
4 + 2 = 6
Date Posted:
1 month ago
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