Page 13 - 新思维数学活动用书8 样章

2 Expressions, formulae

and equations

2.1 Constructing expressions

Exercise 2.1 Key words

equivalent
Focus
You can write an algebraic expression by using a letter to represent an expression
unknown number. unknown

This bag contains x balls. Look at the different expressions that could be
written about the bag.

I add 2 balls, so I take 3 balls out
there are now x + 2 which leaves x – 3

I add 4 balls, so I take 5 balls out
there are now x + 4 x balls which leaves x – 5

1 This bag contains y counters.

Match each statement on the left with the correct expression
on the right.
The first one is done for you: A and ii y counters

A I add 1 counter to the bag, so there are now i y − 8
B I take 1 counter out of the bag, which leaves ii y + 1

C I add 5 counters to the bag, so there are now iii y − 5

D I take 5 counters out of the bag, which leaves iv y + 8
E I add 8 counters to the bag, so there are now v y + 5
F I take 8 counters out of the bag, which leaves vi y − 1

12