Question 509429
Let {{{x}}} = kg of cement to be added
given:
{{{ .22*250 = 55 }}} kg of sand initially
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{{{ (x + 55) / (x + 250) = .25 }}}
{{{ x + 55 = .25*(x + 250) }}}
{{{ x + 55 = .25x + 62.5 }}}
{{{ .75x = 7.5 }}}
{{{ x = 10 }}}
10 kg of sand must be added
check:
{{{ (x + 55) / (x + 250) = .25 }}}
{{{ (10 + 55) / (10 + 250) = .25 }}}
{{{ 65 / 260 = .25 }}}
{{{ 65 = 65 }}}
OK