A concrete mix has the ratio 1 part cement, 2 parts water, and 3 parts sand. How much water can be used if 78 kg of sand and 21 kg of cement are available? How much concrete can be made?

Question

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Answer 1

A concrete mix has the ratio 1 part cement, 2 parts water, and 3 parts sand. How much water can be used if 78 kg of sand and 21 kg of cement are available? How much concrete can be made?

Ratio of cement:water:sand = 1:2:3

​We have 78 kg sand and 21 kg cement

​But, ratio of cement:sand is 1:3 = 21:63

​i.e. for 21 kg cement we only need to use 63 kg sand (the remaining 15 kg sand is not used - perhaps next time!)

Ratio of cement:water is 1:2 = 21:42

Therefore we should use 42 kg water.

Total mix is 21 + 42 + 63 = 126 kg

Amount of concrete made is 126 kg