1.7-1.10 Ratios, accuracy, standard form, units

Front

PROCESS:

Share a number into a given ratio

e.g. Share 50 sweets in the ratio 3:2:5

Back

Add up the ratio

Divide the total number by the total ratio; this is what 1 ratio unit is worth

Mutliply the number of ratio units by this value.

e.g. 3+2+5 = 10

50 / 10 = 5

So 1 ratio unit = 5 sweets

Ratio 3 = 3x5 = 15 sweets

Ratio 5 = 5x5 = 25 sweets

Ratio 2 = 2x5 = 10 sweets

Front

PROCESS:

Put a ratio in its simplest form.

e.g A has 20 sweets and B has 16. Write the ratio of sweets A:B in its simplest form.

Back

Treat just like a fraction.

Put one / other in calculator and write the two numbers as X:Y

e.g. 20 / 16 = 5/4

Ratio = 5:4

Front

Significant figures

Back

Count the digits starting with the first one that is not zero.

e.g. 125 is 3 significant figures

0.034 is 2 significant figures

Front

Decimal places

Back

Count the digits, including zeroes, after the decimal point.

e.g.

13.45 is 2 decimal places

1.005 is 3 decimal places

Front

Upper and Lower Bounds

e.g. 15km to nearest 1km

Back

Take the degree of accuracy, halve it and add to / subtract from the original number.

e.g. 1km / 2 = 0.5 km

Lower bound = 15 - 0.5 = 14.5km

Upper bound = 15 + 0.5 = 15.5km

Front

PROCESS:

Estimate the value of a computation

e.g. Estimate (46 x 17) + 11,400

Back

Write all numbers to 1 significant figure, then put in calculator. Do not round your answer.

= (46 x 17) + 11,400

= (50 x 20) + 10,000

= 1,000 + 10,000

= 11,000

Front

What is Standard Form?

Back

Writing a number as

a x 10ⁿ

a has to be between 1 and 10

Front

PROCESS:

Converting time from decimal to hours and minutes

e.g. what is 2.3 hours in hours and minutes?

Back

Number before the decimal is the hours.

Decimal part x 60 = minutes

e.g. 2.3 hours is 2 hours and (0.3 x 60) minutes

= 2 hours and 18 minutes

Front

How many centimetres in a metre?

Back

100

Front

How many millimetres in a metre?

Back

1000