SOLUTION: 438 square yards of wall are to be covered by 24 square foot sheets of plasterboard. Allowing 15% for Waste how many sheets of plaster board are required? I've done 438 square yard

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Question 1045624: 438 square yards of wall are to be covered by 24 square foot sheets of plasterboard. Allowing 15% for Waste how many sheets of plaster board are required? I've done 438 square yards to 3942 square feet. Then devided by 24 to get 164.25 boards however I am not sure about the 15% for waste. Should I devide by 85 and then multiply by 100 to get 193.24 as a final answer?
Thank you for your assistance.
Answer by josgarithmetic(39623) About Me  (Show Source):
You can put this solution on YOUR website!
...24 square foot sheets of plasterboard. Allowing 15% for Waste,...

The indication is that the plasterboard item is big. Not 24 of 1 square foot sheets; but instead, some number of 24-square foot sheets.

NEED TO COVER 438 SQR.YRDS. How many plasterboard sheets minimum?
438%2Ayard%2Ayard%2A3%2A3%2A%28foot%2Fyard%29%28foot%2Fyard%29
438%2A9%2Asqft
3942%2Asqft
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The amount of plaster board used must include 15% wasted plaster board.

ALLOWING 15% WASTE
(This seems to be how you want most of your help.)
100-15=85
let b stand for how much surface area of the plasterboard actually used.
0.85%2Ab=3942----accounts for the amount of non-wasted board.
b=3942%2F0.85
b=4637.647%2Asqft-----reasonably enough near to 4637 square feet

HOW MANY OF THE PLASTERBOARD SHEETS?
24 square feet per 1 sheet.
4637%2F24
highlight%28193%2Asheets%29

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Your work and results are good. The only real trouble is the excessive accuracy. Cut to three significant figures. You could even cut it to just two significant figures and maybe say 190 sheets. The 193 may be better.