An alloy contains 30% of copper, 30% of zinc and rest nickel. The amount of nickel in 400 gm of alloy is :

1. 40% of 400 gm

2. 30% of 400 gm

3. 70% of 400 gm

4. 400 gm - 30% of 400 gm

A number is first decreased by 40% and then increased by 40%. The equivalent change is :

1. nothing

2. 16% increase

3. 16% decrease

4. 8% increase

80% of 200 - 50 is equal to :

1. 30% of 200

2. 110

3. 80% of 150

4. none of these

A number 80 is wrongly taken as 100. The percentage error is :

1. 20%

2. 25%

3. $\dfrac{100}{80}\times 100\%$

4. $\dfrac{80}{100}\times 100\%$