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Answer:
1 kg of sand
Explanation:
For 180 kg of concrete using the given ratios, you need ...
(3/12)(180 kg) = 45 kg of cement
(2/12)(180 kg) = 30 kg of sand
(7/12)(180 kg) = 105 kg of gravel
The inventory of 29 kg of sand is 1 kg short of the amount needed.
Henry is short 1 kg of sand.