Quote:
Originally posted by Liana
omg I didn't know there was a homework thread
please please please can someone help me with math I SUCK at math & physics
1. A uniform metal disc of diameter 15 in. weighs 12 lb. For the purpose for which it was intended its diameter must be 14 3/4 in. and it's weight 11 lb. When it's diameter is reduced to the required size it is still too heavy and it is proposed to reduce the disc to the required weight of 11 lb. by drilling through it a number of 1/4 in. diameter holes. How many such holes must be drilled?
- do you have to find the area of the metal discs or can you directly work with the diameter?
2. A man borrows £1,640 which, together with the compound interest at 5% per annum, he is to repay by two equal annual installments, the first of which is payable one year after borrowing the money. Calculate the value of each installment.
This is due in two days and I'd highly appreciate some help
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For question 1:
First you calculate, the weight per unit area of the metal:
w=12/(pi*7.5^2)=0.67906 lb/in^2
Then you multiply by the area of the new diameter:
w*(pi*(14.75^2)/4)=11.6033... lb
We need it to be 11lb, so we need to remove about 0.603 lb.
Now we calculate the weight of 1 of the small circles:
w*(pi*0.25^2/4)=0.03333...
Then you divide 0.6033/0.0333=181
So you need 181 holes.
For question 2:
Interest formula: (compund annually)
1640*(1+r)^y=1640*(1.043)^2=1784.1 (whatever unit)
We divide this amount by two to get the amount he should pay annually since they are equal amounts.
SN: Not sure about the second question