Basic Simplification Quiz Set 018

This is a multiplication by 9. Proceed like this: 480 × 9 = 480 × (10 - 1) = 480 × 10 - 480 = 4800 - 480 = 4320. Sometimes, the options can be ruled out by examining the units places, but for simpler cases these shortcuts will help you save time overall.

This is a multiplication by a number whose units place is 9. Proceed like this: 226 × 49 = 226 × (40 + 9) = 226 × (40 + 10 - 1) = (226 × 40) + (226 × 10) - 226 = 9040 + 2260 - 226 = 11074. The other approach could have been 226 × 49 = 226 × (50 - 1), etc.,

We have to find $34{1/2}$ × ${68/69}$, which can be written as ${69/2}$ × ${68/69}$, which simplifies to 68/2 = Rs. 34.

If x is the amount, $x/15 - x/21 = 18$, which can be re-arranged to get x = ${18 × 21 × 15}/{21 - 15}$ = Rs. 945.

The maximum occurs when the value of |x - 8| is the lowest, which is 0, so the maximum value is 64.