Question 1029153
{{{ x }}} = number of months
{{{ 50 - 6x = 40 - 4x }}}
{{{ 10 - 6x = -4x }}}
{{{ 2x = 10 }}}
{{{ x = 5 }}}
In 5 months he has same number red and blue notebooks
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check:
start: 50R & 40B
1 mo: 44R & 36B
2 mo: 38R & 32B
3 mo: 32R & 28B
4 mo: 26R & 24B
5 mo: 20R & 20B
OK