Hi there amathsnovice,
Engineers: 4/5 of 180 = 144. This was 80%
Sales: 1/5 of 180 = 36. This was 20%
For the new Sales figure to be 25% then the new Engineers figure should be 75%. Do you follow? So let's find the new total amount given this information. We know there is to be no additional works in the Engineering department therefore we can solve
75% of x = 144. x will be the total number of employees and the new number of Sales will be x-144. Therefore the increase of desired Sales staff will be (x-144)-36.
What do you get?
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