Numerical tests lean on percentages, and the quick way is to build them from easy pieces. Start with 10%, which is the decimal point moved one place: 10% of 340 is 34. Everything else comes from 10%, 5% and 1%. 15% is 10% plus 5%, 35% is 30% plus 5%, and 4% is four lots of 1%.
Two more tricks save time:
- x% of y is the same as y% of x, so 4% of 75 is 75% of 4, which is 3.
- Learn a few fractions by heart: 1/8 = 12.5%, 1/5 = 20%, 3/8 = 37.5%, 1/20 = 5%.
Ratios are shares. To split 240 in the ratio 3:5, add the parts (8), find one part (30), then multiply: 90 and 150. To find what percentage one number is of another, divide the part by the whole: 18 out of 72 is 18/72 = 1/4 = 25%.