Page 27 - 新思维数学活动用书7 样章

2 Expressions, formulae and equations

16 A cookery book shows how long it takes to cook a piece of meat.
Where:
Electric oven T = 70W T is the time, in minutes
W is the weight of the
Microwave oven T = 28W
piece of meat, in kg.

a How much longer will it take to cook a 2 kg piece of meat in an electric oven than in a
microwave oven?
b A piece of meat takes 1 hour and 52 minutes to cook in a microwave oven. How long would
this same piece of meat take to cook in an electric oven?

2.3 Collecting like terms Key words
collecting like

Like terms are terms that terms
contain the same letter. like terms

The letter in an expression represents an unknown number but, if you simplify
find it easier, you can think of the letter as an object. term

You simplify an expression by collecting like terms.

Example: a + a = 2a Tip
2b + 3b = 5b 2a and 3a are like
terms. 2a and 3b
are not like terms.
Exercise 2.3
Think of a as an
apple, so
Focus

1 Match the expression in each rectangle to its correct simplified
expression given in the oval. Think of b as a
The first one has been done for you: A and iii. banana, so

a + 4a a + a 3a + a a + a + a 5a + 4a 2a + 2a + 2a

A B C D E F
9a 3a 5a 6a 2a 4a
Tip
i ii iii iv v vi
Remember that a
means 1a.

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