How do you calculate it?

Question

A factory manufactures products in two grades of quality. 90% of its revenues comes from manufacturing the first-rate product. How will the revenues change if production of the first-rate product is increased by 10% while the production of second-rate product is decreased by 10%?

"What have you tried?" ... I've voted to close for lack of work shown. — The Chaz 2.0, May 26 '17 at 19:18
I have really no idea how to get a equation from the question. — maki, May 26 '17 at 19:19

score 3 · Accepted Answer · answered May 26 '17 at 19:27

3

$$90\%\cdot r=r_1\implies10\%\cdot r=r_2$$

$$r'=110\%\cdot r_1+90\%\cdot r_2=(110\%\cdot90\%+90\%\cdot10\%)\cdot r$$

answered May 26 '17 at 19:27

score 1 · Answer 2 · answered May 26 '17 at 19:21

HINT

Say current total amount is $m$. Let $x$ for first-rate product, $y$ for the rest.

Step 1: could you show what $x,y$ are in terms of $m$?

Step 2: what is $x$ increasing by $10\%$, and what is $y$ decreasing by $10\%$?

Step 3: what is the new total amount in terms of $m$, and could you find the new percentage now?

How do you calculate it?

2 Answers2