If $${b\over a}=0.7$$ find the value of $${a-b\over a+b}={11\over34}.$$

Find the sum of 2x terms of the series ( 1² - 2² + 3² - 4² + ___ ) 

Direction: Study the following information to answer the questions.

In hotel B, the ratio of female customers on Tuesday and Friday was 2 : 3. If on Friday, female customers constituted 50% of the number of customers (male + female), then what was the number of customers (male + female) in hotel B on Friday?

Wheat costing Rs. 30/kg, Rs. 35/kg and a third variety of wheat are mixed in the ratio of 3 ∶ 4 ∶ 2. If the mixture costs Rs. 34/kg, then what will be the cost (in Rs./kg) of the third variety of wheat?

If a shopkeeper buys 2 oranges for Rs.5 and sells 3 for Rs.7 only, then what percentage of loss and loss did he gain?

An aero plane flying horizontally at a height of 3 km. Above the ground is observed at a certain point on earth to subtend an angle of 60⁰. After 15 sec flight, its angle of elevation is changed to 30⁰. The speed of the aero plane (taking √3=1.732)

A trader marks his goods at 20% above cost price. If he allows a discount of 5% what is his final profit%?

What will come in the place of question mark (?) in the following question?

  $$?=5\sqrt{ \left(243 \right)^2}$$