To add GST…

To add GST multiply by 1.15 the 1 is for the original amount, the.15 is 15% GST Eg: $50 plus GST = 50 X 1.15 = 57.5 giving the answer of $57.50

To take off GST…

To take GST off an amount divide by 1.15 Eg: if $115 is the sale price including GST, the price excluding GST is 115/1.15 = 100 giving an answer of $100

To get a percentage of an amount

multiply the amount by the percentage and divide by 100 Find 24% of 87m, 87x24/100 = 20.88, round to 21m [including units]

To get a fraction of an amount

multiply the amount by the top number, then divide by the bottom number. Find 2/7 of $87, 87x2/7 = rounding to $24.86 [including units]

To split a number by a ratio

Take the number you are spliting and times by the first ratio number then divide by the ratio numbers added together. Take the number you are spliting and times by the second ratio number then divide by the ratio numbers added together. The order of the values matches the order of the words in the question. Split 40 people into a ratio of girls to boys of 3:5; 3+5=8; 40*3/8 = 15; 40*5/8 = 25 Ans 15:25 15 girls; 25 boys