Which out of the following are expressions with numbers only?

(a) y + 3

(b) (7×20) – 8z

(c) 5(21-7)+7×2

(d) 5 (e) 3x

(f) 5 – 5n

(g) (7×20) – (5×10) – 45 + p

To find sum of three numbers 14, 27 and 13, we can have two ways:

(a) We may first add 14 and 27 to get 41 and then add 13 to it to get the total sum 54 or

(b) We may add 27 and 13 to get 40 and then add 14 to get the sum 54.

Thus, (14 + 27) + 13 = 14 + (27 + 13).

This can be done for any three numbers. This property is known as the associativity of addition of numbers. Express this property which we have already studied in the chapter on Whole Numbers, in a general way, by using variables a, b and c.

Make up as many expressions with numbers (no variables) as you can from three numbers 5, 7 and 8. Every number should be used not more than once. Use only addition, substraction and multiplication.

Identify the operations (addition, substraction, division, multiplication) in forming the following expressions and tell how the expressions have been formed:

(a) z + 1, z – 1, y + 17, y – 17

(b) 17y , , 5z

(c) 2y + 17, 2y – 17

(d) 7m, - 7m + 3, -7m – 3

Give expressions for the following cases:

(a) 7 added to p

(b) 7 stbtracted from p

(c) p multiplied by 7

(d) p divided by 7

(e) 7 subtracted from –m

(f) -p multiplied by 5

(g) -p divided by 5

(h) p multiplied by -5